Some years ago there was a period of time where it was kind of common knowledge in the industry that Uma was not a great person to work with, or even just be around.
Apparently, Uma was constantly using really racist language, behaving very selfishly, being really rude and mean on sets, was drunk and stoned all the time, and always acting like she and her boyfriend were king and queen shit.
Other female industry stars distanced themselves from her as friends, and there was cat-fighting, drama, and wars of words on social media.
During this time studios and production companies would not hire her, either.
These were accounts of a specific time in her life, though, and Uma has most likely moved passed all that.
However, she does work in "the oldest industry in the world", and some revue sites do have postings about her being extremely hard to deal with.