SOAPUI - NullPointerException occasionally occurs when running test suite.

Hi bgoldsto​ 

Ensuring no concurrent edits of endpoints or properties during request execution is a best practice to prevent NullPointerException caused by missing request URIs. Running TestSteps sequentially as a test is an effective way to verify if concurrency is the root cause of your issue and can often solve this problem

Hope this helps - Happy to help further!!
Thank you very much and have a great one!
Warm regards