I have a Content Type Hub where I created about 10 Content Types using several Site Columns. One of the Site Columns was set as a DateType type rather than a Person or Group type. The Content Types were already published and consumed by a document library in another site collection before I realized my mistake.
Of course I couldn’t just change the column type from DateTime to Person or Group and expect it to just work. We don’t even have the option to try.
In order to fix this I had to remove the column from each content type in the Content Type Hub, delete the column, recreate the column and add it back
to the content types.
Of course republishing at this point failed because there was a conflict in the columns on the main site collection with what is now in the Content Type hub.
Furtunately I was able to just delete the library, mark the content types as read-only in the site collection and then delete them. Next republished the Content Types from the hub and finallly rebuild my library.
It wouldn’t have been so simple if I had real content that I couldn’t delete.
The moral of the story is to make sure your content types and site columns are correct from the beginning! It will save you a lot of time later on. I was lucky to catch it early on as I was building out the site.