I know this post is old… very old indeed! but the problem persists…
The reason for this to happened is still unknown to me, at some point some objects in the embedded library appear as deleted and you cannot do anything with them, although they remain in the project as placed and instantiated, I eventually found a way to fix it.
First: duplicate the objects and re-link the placed/instantiated copies in the project (by selecting the objects and opening the settings dialog “T” “Command T” or “Control T”)
Second: Release everything and close the project, you don’t need to leave the project.
Third: Open the local data manager (menu: teamwork/project/teamwork data manager) and deleted your local data.
Forth: Open the teamwork project again, it will download the project as is on the server, without those deleted objects 😉
iMac 27 2014; 3,4GHz quad core i5; 24Gb 1600 MHz DDR3; 2 GB NVIDIA GeForce GTX 775M
macOS Catalina 10.15.7
Make your life Custom not Standard. GDLing since 2018.