Yeah, that’s almost certainly the case. I don’t have much more I can offer for troubleshooting tips at this point, as like I say we don’t have anything on file for symptoms like this. Content issues, where they occur, typically result in an immediate crash (say for example, a bad web page or corrupted PDF). And it must be content, since the basic project import test barely imports anything other than content (as you noted, even the icons were not imported).
Again I think we would need live forensic data to really proceed in debugging it. If you cannot share the project as it stands, and you have another machine (or boot volume) you can use to open it with, there is a procedure to scramble the content of a project. As I always stress when doing so, make sure the problem still persists after doing so. I would omit step 6 in this particular case, as non-text content may be the culprit.