From the Open Cities readme:
Known Issues
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When starting a new game if you are using "Knights - Unofficial Patch.esp" you need to disable this until you are able to save and then you can reactivate it. This is due to a bug in how the UOMP handles reverting some changes for previous Open Cities compatibility scripts that don't need to be run during chargen.
The game crashes a couple seconds after you finish creating a character if you don't follow this. I suppose deactivating the master would work as well, which is probably why you had this note.