I see that manual update is turned off. It should update in real time.
Seems like it is a problem with 3ds max,- not ForestPack. Has it always been this way? What changed since it was working correctly?
One thing i can suggest to try is to rename Your ENU folder at this location:
%localappdata%\Autodesk\3dsMax\2020 - 64bit
If that wont fix the issue, You can delete new ENU folder and rename back renamed folder to "ENU"
Let me know if that helped.