Flaky tests (non-deterministic tests) are useless

"Non-deterministic tests have two problems, firstly they are useless, secondly they are a virulent infection that can completely ruin your entire test suite. https://martinfowler.com/articles/nonDeterminism.html" Source Twitter

I think that statement summarizes the problem very well and the linked article by Martin Fowler explains that statement very well - so I would recommend to everyone to read the article. Although it was written in 2011 the listed kind of problems are still the same.