Hey,
I have same issue. I think it was happened after last update (15.0.2) or maybe right after update ios15. I’m not sure.
Anyway, iPhone (7) Storage shows me reminders - data and documents (5.55 GB). The total occupied storage of the iPhone is 22 GB, but after connecting the iPhone to the Mac, it shows 24.5 GB
iPad Pro - reminders 4.05 GB
Apple Watch Series 3 - reminders - 3.99 GB
I deleted everything in reminders app…
I've already canceled sync of reminders with the cloud and deleted all reminders data (it was around 3.7 GB)…
I have already tried reset my phone and then restore from backup… but nothing worked
I also checked icloud on web and reminders doesn’t work there (Perhaps it is because of unsychronization, don’t know)
Do you have some tips how figure out this issue? It is really annoying and main problem is my watch… I can’t use it properly
because of full storage