Limit on the number of child items was reached

I got this error and thought there must be an explanation here but nothing could be found.
So what does this error mean?
“limit on the number of child items was reached”
It shows up in the bottom left of Joplin screen on the PC above the synchronisation symbol.

Could you check the synchronisation status screen? How many total items do you have?

Sync status (synced items / total items)
Note: 10944/11451
Folder: 5/5
Resource: 10189/10063
Tag: 3850/3850
NoteTag: 122994/122994
MasterKey: 1/1
Revision: 1999/1843
Total: 149982/150207

Conflicted: 3
To delete: 199

Hmm I guess the limit is 150,000 items on OneDrive then. I can think of a fix, but it’s nothing trivial so it won’t happen soon.

Do you have many tags per notes in general (it seems there’s 120K tags for 10K notes)? If not, it might be left-over tags which can be deleted.

To do that, the only way is to export each notebook individually. Then clear your local profile data, clear the sync target, then re-import and sync again. Exporting the notebooks one by one means the left-over tags should be deleted.