Hello Maxence,
These type of errors usually occurs when you are moving/copying/transferring the .aedt file to some other file location without archiving it. This may cause model corruption because of .aedb folder and related file loss. While creating the model, you might have used other Design Tools in the same project like Circuit design etc. and those design information will be present in the respective .aedb file. You always need the tail folders for a non-corrupted model, no matter you found the model picture intact on the Thumbnail view.
Regards,
You are navigating away from the AIS Discovery experience