Well the issue is not as bad as before but it is still happening. Yesterday I was moving the cutoff knob in the HALion 6 GUI (in the instrument panel, not the dedicated cutoff knob at the bottom of the interface), I was moving it a lot trying to find the perfect spot while FL Studio 20 (version 20.0.3.532) was playing (looping over and over) in Playlist mode and again, FL Studio 20 froze and I could no longer interact with the program and had to shut it down user Windows Task Manager.
I also own UVI Falcon and I tried doing some heavy knob turning (cutoff and other modulations) in FL Studio 20 (while the sequencer was looping) and everything was fine. It did not freeze FL. So it seems that HALion 6 is not getting along well with FL Studio 20 BUT the situation has improved as version 20.0.3.532 seems a lot more stable with HALion 6 as previous FL 20 versions. It’s just that the issue still seems to be there but does not happen as frequently.