Hi there,
I was having the same issue on my new device (Samsung s20) what I was assuming is some sort of bug preventing the authenticator to switch between devices and I decided to give a try to this solution even at the risk of being unprotected for a wile until the issue gets fixed.
I can confirm that in my case login in to my blizzard account, disabling the authenticator and setting up auth app fresh just worked fine.
I can in fact confirm that this worked!
Using the sms protection for the authentications needed, i detached the authenticator from my account on blizzard.com, started the setup process on my blizzard authentication app and everything worked as intended 
!
Thank you sirPapaya 
.
Please don’t close this thread. Detaching an active Authenticator via the blizzard account dashboard works. I don’t want to do that. I want to use my existing serial number and restore code to clone my Authenticator onto another device, to have a backup. IT WILL NOT WORK. Any support staff can get in contact with me and I will screencap my Authenticator showing the serial and restore code, and invite them to attempt to manually restore onto a native app.
I talked to my MVP contact in Customer Support about this last night. He is not part of QA or any sort of developer team though. It has been escalated to get those who are responsible for the Auth app to take a look. Not sure when/if you will hear anything directly. I also don’t expect much traction on a weekend.
I would not give up hope though. They really want accounts to be secure.
I have a similar issue - mainly that the 2nd phone I try to attach fails. If I wipe the authenticator from the account and set it up anew - it works on the first device I configure it on.
If I take the restore code to a 2nd device, (or even use the login) it spins and then fails immediately with the “unexpected error occurred” [even happened on a fresh phone] If i wipe and set it up on the 2nd device first, it works, but then taking the restore code to the 2nd device fails just as the first one had.
Yes dude, same, same. Even attempting the SMS protect based restore on the second phone fails? It “acts” like it’s going to work, then errors out and goes back to the login screen?
TL;DR: The issue was “resolved” by removing the authenticator and then adding the new one from the new phone.
I contacted their support, and the answer was that “the authenticator […] is phone specific” and “There is no way to just swap the authenticator from phone to phone”. They said that SMS protect is phone independent, as it’s coupled to the phone number, but using SMS as a verification method is not an option for me, because it’s basically just a digital post card.
So in conclusion there does not seem to be a way around removing the old authenticator from the account settings, and then adding the new one; a support article (can’t add links here, google for “blizzard authenticator switch phones”, first result) states as much.
Here’s to hoping they add an option to just use any common TOTP app in the future 
You guys are lucky… at least you got your old phone still working.
I had my phone die last week, it’s currently in repair but it might not be fixed at all, But I had the Serial & Recovery Code saved up as a screenshot so I should be fine.
yet, trying to add authenticator on a 2nd mobile now so I can login to my account does not work, and I don’t even have access to my old mobile right now to remove the authenticator and add it to my 2nd mobile.
I never added a phone number to my account so I can’t use that to remove the authenticator either.
I got a solution.
#1 Open accountDOTblizzardDOTcom/security
#2 Disable fully authenticator app at the correct section.
#3 Open auth. app on the new phone.
#4 Register it on the new phone
#5 Ur done.
It worked for me, i hope i could help.
If this is now true that is a MAJOR change. A core function of the Authenticator app is that it can be put on multiple devices and moved from phone to phone by using the Serial Number and Restore code. That is the whole point of the Restore function in the Auth app!
Also if they did make such a change, how can we restore our mobile authenticator if the old mobile is dead like mine ?
I didn’t purchase a new mobile, rather my old one suddenly broke without any notice, so I am locked out of half of my account nor can I login from a new device anymore. even though I have my Serial & Restore code backed up.
There wasn’t even any warning about this change from blizzard. (if it is true that is)
I already tried this, but disabling the authenticator app need me to give my authentication code first lol my mobile is broken so I don’t have any authentication code.
No, there was no warning. BUT the Support article now only references the restore feature for iCloud stuff. So, this could be true that the Auth is now device specific other than iCloud.
They tend to be rather secretive about Security things for good reason. However, changing the process to move to a new phone is a big deal. My MVP contact is one of the Forum Support Agents for the Customer Support forum where they handle helping folks with questions and policies. He did not know about this. None of the other Tech Support MVPs knew either so it had not popped up for us yet.
I will do more checking on Monday once folks are back to work. IF this is true and we really can’t restore to a different phone the Auth OR put it on more than one non-apple device at once, it is a major change.
it is indeed a major change and it kind of make the whole Serial and Recovery Code function pretty useless.
I mean what is the use of backing them up, if you can’t use them without having access to your current authenticator ? in fact you can get them anytime you want if u have your authenticator, so there is absolutely no reason the application tell us to back them up lol
but fortunately for me, I just remembered my very old cheap Chinese tablet I bought 5-6 years ago for 50$ and didn’t use it for years now, still have my Blizzard authenticator in it lol
After turning it on I was able to get my authentication code and use it.
there is no one-click function, probably due to it being a very old version of authenticator app. but the code alone fixed my work.
Please keep on top of this, this is very important to me. I have a working, valid active authenticator and I just want to have a spare code generator on an old android phone.
Same situation here, with an interesting twist. I have a Samsung Galaxy Note 9 that was always running the authenticator correctly, and all was well. I did a factory reset, and a fresh load of the phone, and at that point, the authenticator refused to restore.
Interestingly, I was encrypting the external SD card at the time, and all of the attempts I made to restore the Authenticator failed while that was running. (My Starbucks app failed to reload my gift card, too, interestingly.) But literally the moment the encryption completed, I rebooted my phone, and was then immediately able to get my authenticator to restore.
During encryption the external SD card is marked as both available and offline, so I wonder if that was confusing the app somehow. This is probably an edge case and I’m reporting it to Blizzard, but just wanted to state that the lock on the external SD card appears to be related, and the release of that lock solved the issue.
Or maybe it was just the reboot… but still a strange coincidence.
Thank you. With the notification of your post and your success at restoring I went ahead and tried again. It works now!
Heads up MissCheetah: sounds like the initial response that was reported about the Authenticator not being transferable was not true.
For technical details, I didn’t “need” to use the restore codes, in the android version I had to sign in, get sent an email challenge code, provide that, and my Authenticator restored appropriately. Both my primary iPhone and this spare android are now displaying the same TOTP code as well as serial number info.
I think that behind the scenes the blizzard service was not functioning correctly and it’s now fixed.
I no longer need help on this issue but I wasn’t the one who started the thread. Please follow up with that person.
Not sure if something changed on Blizzard’s end, but today everything started working again and was able to restore my authenticator to more devices (using both restore code and login)
Nice dude. It was definitely on Blizzards end. Same experience as you with nothing changing in my configuration.
Really!?! Yay!
I sincerely hope that escalating this fixed it. I wish I could get actual answers but my contacts are all front facing forum folks who have nothing to do with the security side.
Still, progress and updates are good!
This thread was very well done with clear explanations, troubleshooting steps you took, updates, etc. Those who have to fix errors appreciate it a LOT.
Fingers crossed all is better now.