Okay,
So I was able to replicate the issue in TinkerCAD but not Meshmixer or Inventor. My Cura (4.12) is also not displaying any errors. Could you try slicing one of the mounts and check it out in previews to see if the layers are going to print as intended? I think the issue has to do with the way the models are generated with separate parts and the variations between how different modelling software interprets it. I have a possible solution in mind and will work on hopefully implementing it here shortly.
As for the manual value entries, yeah there is a bug where they are either 5mm too much or 5mm to little, I have already fixed this and will include it in the next update. When in doubt, the number displayed above the slider is the actual bolt offset. For some stupid reason, I forgot to do the math to account for mesh dimensions. The sliders do not move when using manual entry, I may change this but currently it does not due to the size cap on the sliders to allow for accuracy. For example you can enter 100.0101mm but the slider would only go up to 60mm and wouldn't reflect your manual entry, I may change how this works in the future.
I apologize for the issues you are having and thank you for helping me work through them, I'll do my best to implement fixes shortly.