I believe there is a bug happening when you confirm a registered email on a window that is logged on with a different bot than the one you are confirming the email for.
It seemed to add the email to this bot as well, however when I checked which bots were registered with the email on this bot it claimed there was only 1 bot, when there should have been 15. So I removed the verified email from this bot and now when I tried to add an email I get error 500 on this bot. The other bots attached to the email work fine.
discord