I missed this thread and started a new one. I'm having same problem. Have copied and pasted my message from that thread:
Have been having this problem for a couple of days now. Was logged in to test server checking out Valentine's event when I got kicked off game and had message to refresh. Tried it but would not reload. Since then have tried various browsers, cleared cache etc but still keep getting this message every time I log on https://prnt.sc/xgsjax
Every time I click green tick to refresh the game refreshes up to same point then brings up exactly the same message effectively locking me out of game on test server. Not having this problem on proper server (touch wood!) but would be nice to finish testing new event.
ETA: I think I was upgrading some wonderous residences with gems when I got kicked off and haven't been able to log on since. My session had probably been open for about 30 mins at that point. I was using the Opera browser.