Disclaimer: I neither have SWAM nor any MPE controller, so it’s just guessing:
I think the behaviour you describe might be related to how dynamics are created from classic MIDI controllers vs MPE controllers. So normally you have note on velocity plus arbitrary other controls while controlling the stringed swam instruments with MPE may rely on press input to control dynamics while ignoring the note-on velocity.
Have you tried the templates this guy here suggests?
Also, I don’t know if by default the “bow pressure” is mapped to that aftertouch parameter like this guy suggests.
I really hope it’s something like this and that your controller just doesn’t have wear…