Well, I did that many times and still get it. If I don’t log in (use it offline), then it goes away. Why? I’m using it in my updated 64-bit W10 Pro. PC. I even tried rebooting my PC.
I also have two different battle.net accounts too. I only noticed it in my accounts with full versions of Diablo games including 4 UE that I just redeemed yesterday via the web site. I haven’t downloaded it yet. Is this why?
Thank you for reading and hopefully answering soon. 
Hey there,
So the core issue is the Desktop App wants to do an update (specific to a license you own on the affected account) but is being blocked or interfered with by something with the desktop application, the client in question, the network/connection, software on the system or the system itself.
The easiest thing to do is a clean removal and reinstall of the desktop application and its support files and retry.
If that doesn’t help, you can then try the following:
Try doing an extended power cycle on your system. Turn off all devices including the modem. Wait 30 minutes, turn on the modem, wait 5 minutes, turn on any network devices, wait 2 minutes, turn on your computer and try the game.
You can try switching your DNS settings to use a free public DNS servers instead of your ISPs Servers:
We do not have individual steps for specific modems or routers so if you need assistance accessing or updating the devices, contact the device maker/provider.
Sometimes firewall or routing software/hardware will have some advanced settings to prioritize and manage types of network traffic. Normally that is not an issue but we have seen situations where it can interfere with the delivery of the data for our games/voice chat.
Let’s try turning off these features:
QoS
SIP ALG
RoG (ASUS Routers Only)
Security firewalls (Some ISP provided modems)
Not all devices will have these options and the steps for turning these functions off will be different depending on the make/model/software version of the devices and programs involved. If necessary look at the documentation for your security and routing products to find out how to turn these options off.
In some cases there is a corrupt or misconfigured setting within the router or modem. We cannot say what that might be offhand but the easiest way to resolve these conflicts would be to factory reset the router and/or modem.
You may need to look up your specific model for the steps on how to do this and in some rare cases you may need to have this done by the ISP. Feel free to reach out to them for assistance if necessary.
Try running your system in selective startup mode: https://battle.net/support/article/200483
Create a new administrator account: Blizzard Support - Creating a New Administrator Account
Once the account is created, shut down the computer, wait 60 seconds, restart, log into the new profile and try the app/client.
If that doesn’t solve the issue, then I recommend submitting a ticket with an msinfo attached for further investigation. (instructions for collecting that msinfo report will be on the form.)
Click your name at the top right of this page, click support, click contact support.
Will I have to redownload, reinstall, and reconfigure my games when I do this? My new D4:UE game works fine even with this older Battle.net version.
Also, how come my forum thread doesn’t e-mail me notifications? I only get them in my web browser when logged in. Did I miss an option for it?
Having same “Restart and Update” constantly show in the app using Wine on linux.
Sometimes I just see the Battle net .exe’s just hang after exit forcing me to stop them.
Sometimes I get a clean exit and restart.
But in both cases, still shows “Restart and Update” after the app starts again.
I’ve tried:
ProgramData/Blizzard Entertainment/Battle.net/Cache/
These are the versions of the folders I see:
Program Files (x86)/Battle.net/: Battle.net.beta.14216, Battle.net.14215
ProgramData/Battle.net/Agent/: Agent.8209
I am still having this problem. 
@Ant The last part of my response included a request to submit a ticket if those steps did not help but it does not look like you have done so.
Make sure you have completed all the steps presented and if the issue persist submit a ticket.