Looks like the CloudKit sync issue in *OS 26.4 is real (I can repro with all of my apps), and has the very distinct potential to lead to catastrophic data loss and/or sync conflicts across effectively all apps. Apps only receive changes from the cloud after being quit and relaunched.

If Apple hasn't pulled 26.4 already, it should do so immediately until there's a fixed build

https://mastodon.social/@lukaskubanek/116299581006179836

@stroughtonsmith
Would our issue have anything to do with this:
We’ve been using Reminders for years as the simplest mutual shopping list. Need something from the store? Uncheck it. Bought it? Check it.
Need something not on the list yet, add it unchecked.
Since 26.4 several items disappeared from the list that have been on it since we’ve created it. Like “Bread”.
I mean, we had to re-index the search in Reminders before (a terrible regression for many years now), but now items are truly lost.