If only Tasks are added to the Loop that are waiting for an Event to be set (or a Lock to be acquired but that makes no sense at all), the loop exits because those Tasks get removed from the main queue and put onto the waiting queue of the Event.
Use-case: Event is waiting to be set from an ISR. Will probably only ever be used without other Tasks running in minimal test-cases but would then be a problematic bug.

Expected behaviour: Loop continues to run. This needs #5795 (Events from ISR). Otherwise this problem will of course never occur.

>>> import uasyncio as asyncio
>>> ev=asyncio.Event()
>>> async def wait():
...     print("started waiting")
...     await ev.wait()
...     print("got event")
...
...
...
>>> asyncio.run(wait())
started waiting
>>>