What gameplay feature is this bug affecting?
Logging in/switching accounts

What's the issue? Please include any error messages you receive and as much detail as possible.
It seems to happen when I access the event page. At first I thought I'd hit the "switch account" button by accident, or had switched absentmindedly. Once, I can assume it was me. But around the 3rd or 4th time, it was becoming apparent, it's probably a bug. I started out in my side account (this one), and, after getting and viewing a "Tournament result" e-mail, I navigated to the event page via the Event Currency Balance button. When I clicked on ""Battle Arena", I realized that I was on my other account. Is this a known bug? I've only noticed it happening today.

Any links relating to this bug? For example, if a particular lion is bugging, what is the link to that lion?
Just the event page

Any screenshots you can provide us with?
No, sorry

Please provide us with step by step explanation how this bug happened so we can attempt to replicate it. If it's complex, please include screenshots where possible:
I started out in my side account (this one), and, after getting and viewing a "Tournament result" e-mail, I navigated to the event page via the Event Currency Balance button. When I clicked on ""Battle Arena", I realized that I was on my other account.