Hi aleksi,
Thanks for getting in touch and reporting this issue.

I wonder if this is related to syncing, since the Apple Watch app may be delayed by up to an hour due to watchOS limitations to sync your changes. But you mention other changes syncing, so maybe that's what you mean? Even after other changes are syncing, that deleted task is still there?

If so, could you contact us so we could get some more specifics? Thanks! 💙