I'm not sure if it's a MusE (4.1 appimage) or a Pianoteq bug:
If a project contains a Pianoteq 8 vst plugin, where, within the plugin itself, I have changed an effect of any preset (e.g. changing delay to fuzz, or chorus to amp), all is fine until I save, close, then re-open this project: then MusE crashes.
As far as I know, this only happens when I change one of the three effects (excluding reverb, which cannot be swapped with another effect), shown in the image below, to another effect. (I can change the parameters without corrupting the project.)
This does not happen with Pianoteq 7, and it only happens with the vst version of Pianoteq 8. The lv2 version seems fine so far. Also, if the vst is used within Carla, with Carla as plugin in MusE, all seems fine as well.
Edit: it seems changing any effect to one of {wah, fuzz, amp} causes a corrupt project. Others seem fine.
Edit 2: I tried it out with QTractor (0.9.29 appimage): no crashes here.
Edit 3: If I create a preset in either in standalone or plugin Pianoteq, with one of the offending effect swaps, then if that preset is used in a project, that will crash MusE at loading too.
Edit 4: If I use a Pianoteq standard preset which by itself uses one of {amp, fuzz, wah} then loading that project crashes MusE too, if not the first time, then the second time.