Hello there.
Recently I had the same problem with Revo 2.0.0 installation (but the other one 2.0.0 worked fine).
Updating to Revo 2.0.2 didn’t fixed the problem.
After that I had totally reinstalled codemirror:
1. package manager > uninstall > second radio button (uninstall or something).
2. remove codemirror’s line from modx_transport_packages table
3. remove both folder and transport archive of codemirror from /core/packages/ folder.
4. download codemirror via package manager
5. install as usually.
6. clear site and browser cache.
And I made 2 or 3 such re-installation rituals until it succeeded. Maybe they had smallest differences in steps, may be not.
I didn’t figured out what was the problem at all and what steps I made was meaningful. It looks like magic to me
Hope it could help.