This is not a 10 vs 11 problem, but apparently improper usage / library management. If you got a message about errors in the lib part in the 3D window, then it is a bug in the lib part.
I've never heard of getting a missing lib part message from the 3D window and not having received the message upon loading the file / 2D.
Open Library Manager and click reload. Does the error report list missing objects? List a few of them here so others can help. Sometimes the error report is not complete after a reload. I have no idea why. Close/save your project also, restart ArchiCAD and examine that error report.
Have you drag and dropped objects off of a web site? Again, look at Library Manager and see if there is anything listed under the blue 'Other' folder. Perhaps with a question mark, meaning that lib mgr cannot find them? (Ideally, one should never have anything under 'other' - but instead should have loaded the AC11 lib folder, your project lib folder (you have one, right?), and perhaps an office lib folder (for student projects this doesn't necessarily apply). Once in a while, specialized libs might also be loaded - but I highly recommend against loading individual parts as oppposed to their containing folder.
Cheers,
Karl
PS I'm really glad to read that ArchiCAD is being used as WSU.
AC 28 USA and earlier • macOS Sequoia 15.3, MacBook Pro M2 Max 12CPU/30GPU cores, 32GB
One of the forum moderators