I'm having the same problem on my iMac 27" 32g ram OS 10.15.7 when using StudioOne Pro ver.5.1 as my DAW.
I have no problems using Logic Pro, Cubase, Mixbus6, or REAPER. SO I believe it's a possible combination of SO configuration, BIAS FX2 ( BIAS FX no problem). The resolution is the same for all DAWs. I've been working with the techs at Positive Grid for over a week. A very important observation, BIAS FX2 VST, and AU run fine in StudioOne Pro Ver.5 on my 2010 MacBook Pro.
This is not an answer but I didn't know how to respond to your post, sorry.