@laurent thanks I can't tell if it's a bug although reading the post here Orphaned revisions it appears we've had an exchange before on this topic and you seemed to suggest old revisions are indeed supposed to be removed from the remote on expiration.
In the end I created a bash script to remove the orphaned revisions on my remote and at some point I stopped using history altogether. I don't know if I'm the only one with this issue (maybe people with a huge number of notes and workbooks don't notice or don't care ... I mean you could live with it) but reading this post I may not be the only one. As far as I'm concerned I'm using Nextcloud (self hosted).
If I can help in any way let me know.