You’ve got a much better chance of getting a helpful answer if you post your questions in the thread for UMA.
Possibly you are using a version of Unity that is too new for UMA to be compatible. While I don’t know for certain how current UMA is right now, my guess is that probably the 2018.4 version of Unity is the latest approved for use with UMA.
The latest reference I see in the release notes is that it is 2018.3 compatible. Which is generally the same thing as 2018.4.