I am now believing that the search is not hung but massively busy because of the cascaded non-greedy search pattern. The search hits on the first 3 specific strings but fails on the 4th specific string parsing a file with 50 cases of these failures. This results in a massive amount of nearly passing patterns.

To solve my "seemingly hung" problem, I added a pre-check to the search string to see that the search is likely needed.

Thanks for your help. This case can be considered closed.