I have been seemingly randomly getting a slowness effect. Its countdown starts at 3 or 4 seconds, counts down to 0, then restarts. It begins with slowness I, but gets stronger over time-- so far the highest has been III or IV.
Is this an intended effect from something in the modpack, or an error? Any idea how I can stop it so I can actually run away from hostile mobs while mining?
When I made my world, there were warnings that some things (datapacks maybe?) were outdated, if that could have anything to do with it.
Thanks!

Edit: It might be related to going underground? Sometimes it goes away when I come back up from mining, but not always.

It happens when you have 2+ sacks in your inventory, it confused me as well

I have the same problem !