Thanks for your help, but that's not help I'm looking for...
This is an update to make it work like before !
I've been doing QR-codes for years...
Even with online software, V5 does not work properly.
The original STL file in this thread sliced correctly in V5.0.1 for me. Go to Edit Process Settings > Advanced tab, and change the Slicing Region Repair Mode to "Alternating Fill". That seems to work better with this model.