We're using pytest-asyncio in a repo with 20000+ tests. With 0.18.0 I get a pytest collection time of about 25 seconds, running pytest . --collect-only. Updating to 0.18.1 increases the collection time to almost 300 seconds.

0.18.1 only contains one logical change, so that's the cause, but I don't (yet) have a clue about a resolution.