Can you let me know if the other mechanisms to Start Game are still functional?
Namely the “Start Game” button from within UEFN, or the start game button that is available in the My Island settings[Located at the bottom of the my island settings page]?
Have you recently added any persistence features? Such as to the following devices:
Save Point
Tracker
Stat Creator
Switch
If this is the case, you can try deleting or disabling persistence on those devices to see if it resolves the issue.
If it is related to that, then we should have a fix for that going out in 30.00.