On a multiplayer server in a standard survival world with all default settings if no loaded chunks will allow for more mobs to spawn in, such as if all blocks in the chunks have been set to air except for a small platform the player is standing on, then mobs will stutter when moving and get knocked back and fall at a slower rate.

I should also add that it occurred when I was the only player on the server. This limits the loaded chunks to the ones that are around myself. I have not yet had a chance to test it with another player online in an area where mobs can spawn.

Added June 8 - I had a similar area at worldspawn where mobs could not spawn but the bug was not occurring in that area. I tried moving worldspawn to the affected area but there was no change. The area still had issues while the original location of worldspawn did not.

The major difference between the 2 areas is I would describe the affected area as 16x16 chunks with the outer most area containing nothing but air for a little over a 3 chunk depth into the 16x16 chunk area leaving what could be considered an island of 9.5x9.5 chunks in the middle. The worldspawn however contains no blocks when the sky meets the void.