Not sure if yours is related to mine. I'm having a dive sites issue that has caused my MacOS version to not be able to sync to Cloud a couple of times. I submitted a email request to reset my Cloud storage and never got a reply, but the Cloud syncing starting working again for a while. However, while recreating the dive site error for a developer, I appear to have messed up the Cloud storage again.
Also, be aware that after I get the Cloud error, I have to go to ~username~/Library/Application Support/Subsurface and move the cloudstorage folder to trash. This removes the local cache of the Cloud dive log and forces Subsurface to rebuild from the Cloud version. This only works if the Cloud version is valid, which is not at the moment for me so I'm waiting for reset.