Unstable test runtime - same code behaves unpredictably

I've recently noticed (based on two of my solutions) that code passing local tests instantly times out on your servers. Upon resubmitting the very same code passes. Below are links to said exercises:
- https://exercism.org/tracks/haskell/exercises/binary-search-tree/solutions/wsgac (successful on 2nd submission)
- https://exercism.org/tracks/haskell/exercises/allergies/solutions/wsgac (successful on 3rd submission)
Also, there's no indication at what stage the test runner times out. It would certainly be more helpful if such information were available.