I assume your colleague has tried a Ctrl+ Q rebuild? If yes, and that doesn't work, I'd say the obvious solution would probably be to create sub-assemblies of the components and mirror them, or just use multiple mirror features. And since those are obvious solutions I'm sure you've already thought of them.
If you're just asking if anyone else has seen that specific behavior, then no, I haven't, but I also rarely use Width mates, so they might be causing the issuel
And yes, rebuilding doesn't help.
Indeed, doing multiple mirror features, as in only mirror some of the entities at the time would help but it's strange that one should need to do that.
Thank you for the input, have a nice one.