About transition from A -> B at 80% issue, I know, and from what I understand, it's a limitation of OBS right know, when it goes near 100%, it switch to the scene B, and set the slider to 0.
In order to disable the switch back, a workaround is to untick the 3rd parameter in the filter settings (French UI in my screen, sorry for that)
View attachment 70958
I'll try to see if something better can be done, but no ETA.
About filters, it works on my side, just some requirement : the filter option should be manually modified in OBS filters parameters so it can be visible in MIDIControl. So you don't have to type anything in the 2 boxes, as it should appear automatically, and you just have to select the filter and the setting.