So apparently one of the recent patch has reintroduced the enemy despawn bug into the game I have been able to recreate it on 3 separate occasions in the same location. Video of said bug below. Hopefully we can get this bug back out as bugs being reintroduced into games by patches never ends well.
It's not reintroduced, it never went away in the first place. I've seen it intermittently every single day (and that includes all the demo days and the week of early access).