SoapUI 5.6.0 (Thanks!)
I have no clue what they did, but version 5.6.0 is running smooth when using a Mac.
I have had not yet had any session that was jammed. I even could run all my tests automatic sequential. This 5.6.0 is a relief compared to 5.5.0 and previous versions (since 4.6.0).
I am very satisfied with this version!😀