I have an update about this problem…
Once we had ways to reproduce the issue, which could only be caused in the web version and iPad, we did do a fix to stop it happening again. But, that didn’t take care of models that already had the problem.
We now have added a fix that repairs groups and components that have the problem already. That fix just went live. If you reopen any affected model, in the web version of SketchUp, the bounding boxes should now be ok.
The same fix isn’t on iPad yet, but will be there in the next update. In the meantime, if you see the problem on iPad, open the web version and load your model, and do a save. Then it should be fixed in the iPad app as well. This works even in Safari on iPad, no need to involve a computer or Chrome on iPad.
The fix also isn’t in desktop yet, so models shared from web or iPad may still show the issue. On desktop it’s easier to repair the group by opening it to edit, then closing it again. The next desktop update will have the fix in it. Meantime, the opening and saving in web would fix the model for desktop as well.