@Squid Already tried and done with that. Also tried on a newly installed Windows 10 Machine.
Also tried downgrading unRaid, tried with a fresh install of UnRaid's latest version, tried with a fresh install of UnRaid's older version, but no luck.
Eventually I had to delete the Share on which this issue existed and created a new share.
PROBLEM SOLVED!
But I had the hassle to backup everything on that Share to another drive. Delete the share and then creating a new one.