After performing a File Version Upgrade from 2009 to 2012 on all the files in our EPDM vault, I have found that many drawings have had all their views set to hidden. There doesn't seem to be any pattern to the behavior.
Solution S-035784 in the knowledge base states that drawing views will be hidden if referenced documents are missing at the time a drawing is saved. I suspect that something in the reference updating that occurs during a file version upgrade is causing this.
Has anyone else experienced this issue?