Thanks for the suggestion, but no need now. I’ve managed to get it sorted. I’ve been exporting individual layers to a new file then checking that for errors. Have narrowed it down to a few potential objects so far. Looking to be (but not conclusive yet) ones I’d scanned with iRhino about a year ago, plus some materials I can recreate.
It looks like the object errors have been there for many months, but the material issues were newer. Probably related to this issue too.
It would be nice to have an audit report list problem items with an identifier which can be searched for (or at least, the layer).
In any case, I’d be reluctant to upload this for your developers to look at. I’ve previously posted 4 bugs, going back 9 months, all still in the queue. I’d be uncomfortable bothering the already overloaded developers with my minor issues.