If any entity(including the player) takes suffocation damage and is completely surrounded by blocks, they will be able to move freely through blocks while taking damage. Flying mobs will go straight up to an air pocket(example: caves and surface)and will move up abnormally quickly during this process.
Unfortunately, I cannot provide and videos or screenshots, thank you for understanding.
Linked issues
is duplicated by 1
Comments 5
MC-211727 can probably be back-resolved as a duplicate of this.
I Cannot provide screenshots or videos.
Try to replicate this bug on your own.
Example: spawn the wither inside some blocks while in spectator mode, the wither will take damage and move up to an air pocket or make its own, if mobgreifing is enabled.
non-flying mobs will gain free movement except for down.
I couldn't replicate it in 1.16.5.
If I summone a wither in solid blocks, it doesen't move and die.
Other mobs with suffocation damage could also not go into neighboring blocks.
Could it be that you have a modded version of Minecraft?
Keep in mind that things like OptiFine and Forge are also "mods" that can change behavior.
Please provide some screenshots or videos of this issue occurring whilst the F3 debug screen is enabled.