alright, so in my hunt for the last plate to summon arceus, i went to the swamp biome to try and find a mega swampert.
about a hour or so in, pokemon basically stopped spawning around me. i opened up the F3 menu, and the entity limit was through the roof, even thought i was the only one on, and not near anything we had made.
i looked up, and i saw
DOZENS of swoobats (or woobats, i didnt really double check) were flying in the middle of the air. i got up on a nearby tree and watched, keeping my camera on them as i opened up a playlist for a few videos in my other screen. i sat there, and they never despawned. other pokemon i see despawn, even right in front of me but the swoobats never despawned.

i figure there must be a glitch in the code where the swoobats were not included in the RNG to despawn per tick.
i have no idea if this is a isolated incident, and i had to run to work and stupidly forgot to grab a screenshot, and i havent had the time today to try and do the same thing again. so this is my first report, if it occurs again ill reply to this post with a screenshot

(also please forgive me as i do not have the forge build version due to it being a friend's private server and she hasnt been on since this has occured, but knowing her it should be one of the later stable versions)
(and there are no additional plugins)

(this post was made three times, please keep this post)

I haven't seen this in any of my test worlds, but I have seen several reports of this happening as of late. If anybody has any additional details, please let us know!

(thanks for the report)