## The problem
Reported in Prefect: ModuleNotFoundError when simultaneously running deployed flows using custom image.
## The fix
ModuleNotFoundError when deployed Prefect flows run concurrently from a custom image: root cause was that load_script_as_module was not thread-safe (shared '__prefect_loader__' module name, sys.path modified without locking, modules evicted from sys.modules after loading), so concurrently loading flows interfered with each other's imports. Fixed in Prefect 3.x: PR #16458 (v3.1.9) added a threading lock and unique module names; PR #17524 (v3.2.14) uses real script filenames as module names and keeps modules in sys.modules. Upgrade to Prefect >= 3.2.14.