Defox I think you have to be running Win10 1903. I don't know that it works with 1803 or 1809
we've had it installed since it's release in August and it was working fine in 1803 up until now!
Right, I know that. What I mean is, I don't think newer versions going forward are going to support 1803. I could be wrong. But I would wager that it might be the cause. Only way to really know would be to either take one of the PC's with the issue and update it and see what happens. Or take a bit to bit copy of said PC and lab it, the then update it to 1809 or 1903 and see what happens. That would probably give better insight as to what is going on. If it still doesn't work after the update then we know it's not the 1803 version of Windows 10 and it must be something else going on. That's where I would start.
I don't have any 1803 machines anymore otherwise I would run the tests for you.