If Opus keeps re-calculating the values in those columns it must be because the NAS is reporting that the files have changed.
Is something actually modifying the files? It's quite strange if not (although some NAS have been known to behave in strange ways).
You could try the notify_debug and shellchange_debug steps in this FAQ if you want to see if the NAS is constantly reporting file changes. (The FAQ is about changes not being received when they should; seems like you're seeing the opposite problem, but the debugging steps are the same.)
You could also try turning off the Detect external file changes on network drives setting mentioned in the same FAQ, in case it helps or reveals anything.