Definition of Exclusions not working

Since I am a developer I want to exclude a couple of directories from constant virus scanning, not only because I know the code being in there but also because occasionally the scanning seems to lock certain files for short periods which can then interfere with build processes as these files are then locked and cannot be removed before a new build.

But - while I know that this has worked without issue before - when I just tried to add a new exclusion not only where there none listed anymore (i.e. the old exclusions have apparently silently disappeared :-( ) but when I define a new one, the entire dialog works fine, I eventually select a folder and hit OK, but that exclusion is then ignored. I.e. nothing appears in the list of exclusions and the whole exercise seems to be ignored!?!

Why is this beast not working any more?

This in on WIndows 10 Pro (1903) with all updates (except the pending feature update 1909) installed.

Compumind said:

May I ask what AV/FW you are currently using?

Sure! Windows Defender

But meanwhile I ran the 1909 feature update and since then things are back to normal, i.e. the former list is displayed again (so they must have survived somewhere - probably in the registry) and I was just able to add the exclusion I originally wanted to add.