In the last few days, I have encountered several similar errors where the same folder is marked “Up to Date” on both sides, but the global states do not match, and as such the synchronisation is only partial.
For instance, the folder on Device 1 has 10,000 files and takes 5 GB. I share the folder with Device 2 and let it sync. After the synchronisation has finished, Device 2 reports the folder as having only 3,000 files and taking only 2 GB. However, both sides mark the folder as “Up to Date”.
I have only encountered the issue in my real systems, but have not been able to reproduce it in my test environment yet. Using STRECHECKDBEVERY=1s on Device 2 seems to fix it though, at least for now.