I created testcase with enum which uses AttributeConverter.

I confirm that in 4.11 this works:

SELECT e FROM Entity e WHERE e.type = com.sample.EntityType.TYPE1

And this not:

SELECT e FROM Entity e WHERE e.type = EntityType.TYPE1

So you are right. Integer value worked before 5.0.3 just by accident and we can ignore this fact because this is not documented functionality.
Maybe some words about this in changelog is still be useful. For those like me who accidentally used this functionality. Maybe not...

I think you can close this issue. Sorry for the inconvenience.
Or maybe use it to implement improvement which allows use enums without FQN (if it does not contradict the specification).