I sometimes see these errors on my server machine. This seems to happen from time to time when Syncthing is trying to clean versions (which is set to once per day). The storage where the folders are located is rather slow, i.e. a 5,200 rpm 2.5" HDD.
Are these anything serious, and if yes, what can be the reason for them to occur? Is there anything I can do to prevent them from happening?