Just wasted quite a bit of time trying to upgrade from 2019 to 2020.1 .

During the migration process I was getting a error that it could not find/access sy_sagepep.m4t in the mas_system folder.   Appeared to be there as best as I could tell   PEP is not even turned on.tom.  After blowing the 2020 install away at least twice I found that  installing 2020 without pu1 resolved the issue.  So it would appear that something in the update is causing the problem.

Not positive, but I believe this was the first upgrade with 2020.1.

I haven't spotted any references to this issue at this time, so hopefully this will save someone else some time.