I read from your other post that you are playing the game on iPad, may I ask which generation of iPad you are using?
I ask becasue I play the game (11.8.1 update) on various iPhones (ranging from 7-Plus to 14 ProMax) and only get occasional Arena drop outs after completion but can still grind seeds for the new plant, I also have friends playing on iPad 9th gen and 10th gen without major issues, so there might have been a compatible bug with older iPads. I know this is not really helping for you as the only people can fix the fault is PopCap. I am hopping your information can provide more insight to the bug so it can be QA checked on next release (assuming QA test on iOS still exist) .