What if think a little bit, just a little bit, and do 2x login on first attempt, then 17x, then rest, or even better, manually press enter in all windows.
It feels random.

Most of the time I can login 20 characters at once and then the other 5 after few minutes, this doesn't always work.

I did daily quests on 25 characters in around 40 minutes.

Then I tried logging in 25 different characters and only 6/25 characters got in.

After 3-5 minutes it allowed 3-5 characters and then again.

After 20+ minutes I still didn't have all my characters logged in and missed WG.

Any official word about this would be nice.