On a Debian 10 box, I see on two Remote Devices (both Android) a number of files of zero size that are shown as out of sync. These have been there for a while so aren’t being sync’d away.
The only way I could find to correct these errors was to create these missing files as empty files, wait for ST to propagate them, delete them and allow ST to propagate the deletions. It all took rather a long time of cutting and pasting the file names but now everything is syncing normally.