When I log in for the first time after booting up Bnet, I DC upon log in 90% of the time. And it’s usually more than one DC. Happens for for 5-10 minutes and if I wait it out, it doesn’t happen. I’ve uninstalled and reinstalled Bnet, no dice.
I’ve had this issue ever since BFA at the very least. I think it started with BFA. And in that time, I have erased completed the WTF And Cache folder resets usually recommended to do first. Doesn’t fix the problem. Was only with my second account- no dual boxing- that it did this. It wasn’t until 8.3 did it start doing it to my main account.
Before anyone even mentions it: in this time period I have switched ISPs, moved across the country, and even built a brand new computer (computer building came first, didn’t fix the problem; moved across the country and obtained fiber internet, didn’t fix the problem) so I am pretty certain it is not on my end in terms of computer and internet. For when my internet acts up, it affects everything, not just first login of the day.
Oh and I’m not the only I’ve talked to that this happens to. They’ve given up trying to fix it.
While removing those two folders is part of a UI reset, it’s not a complete UI reset and can leave behind addons that may also be causing issue.
Unfortunately, the CS forums are not the best place for DC or login issues. If this isn’t moved there anyway, you’ll want to post in the Tech Support forums or reach out to Tech Support directly via a ticket.
Well thanks anyway. Even if the folders are just a UI reset, it usually is what people tell me to do, including GMs as addons can be causes of many things. It’s like wondering why your computer won’t turn on and someone goes “have you tried turning it off and then on” and one has to eye roll.
Just figure I’d be very clear about that so someone doesn’t tell me to do that and think it the solution. If it’s not moved then I’ll just repost then
My point was more that you only took care of two of the three folders necessary when doing a UI reset. Follow the link in my first reply and make sure you’re re-naming/removing the “interface” folder too.
Edit: Look like this got moved from CS to Tech Support for you too 
But even the interface wouldn’t do much, considering as I mentioned, whole new computer with fresh install of everything (the WTF and Cache folder reset was on the other computer when it didn’t work) and different ISP, new router, even fiber internet.
The only logical explanation is something on Blizzard’s end, or it’s one of my addons I use (but not the same data) which doesn’t make much sense as they never gave me trouble. And I’m not the only one with this issue, so idk what addons they use that I use.
We’ve seen time and time again where addons of all different sorts have lead to issues. It doesn’t really matter if it’s never been an issue in the past. Part of standard troubleshooting is to remove them and reset your UI completely. Leaving out the Interface folder means that you haven’t actually done a Full UI Reset. You’re still playing with files that have been altered.
While other people may have DC issues, that doesn’t mean that everyone has the same issue. It also doesn’t mean that everyone has followed the proper basic troubleshooting steps.
I’m glad this got moved to Tech Support. Here’s hoping the folks here can lend further assistance 
Here’s hoping, because a whole new computer with a complete reinstall didn’t help lol