At least for a part of the noise I've made around my assemblies I want to express honest apologies.
It looks like I've underestimated my ability to miscalculate some distances in my sub-assemblies (mainly crankshaft vs. main housings) and one is advised to listen to FreeCAD's Report view, regarding A2plus' solver messages, indicating that 'Max positionerror' and 'Max spinerror' reach really high values, to consider a constraint "braindead" IOW logically wrong.
But on the other hand, it was the easiest way to find it out with this working A2plus to inspect the overlapping parts.
After doing this I was able to add the correct constraints, several previous ones wouldn't have been able to be solved by any solver on the world (except for one that can handle "curvature of space").
Now I'd go at fixing the values and refining parts.
In the attached assembly you'd see quite obvious wrong distances and not the critical ones. I've only made the housings and the crankshaft 'fixed' here, and fortunately haven't needed any dummy parts, it just went straightforward in the order you see in 'Tree view'.
BTW, I've added the "modified solutionToParts()" commit anyways, can be that it helped with manual pre-placement via the Properties (just a subjective impression). I don't get errors since adding and maximum was "Total steps used: 4100" for this assembly.
Thank you for your great work,