I found a few multiplayer swimming bugs. You take forever to sink and sprint swimming seems slow. How to reproduce: Be in multiplayer, and walk into water. You will take a long time to sink.
Comments 2
If you do nothing than just go into water, sinking slowly is probably intended; however, I don't think if you sprint /crouch you sink at the same speed, because it's totally normal that you can use your own force to drag yourself down to the bottom.
See MCPE-32015, MCPE-32031 and MCPE-32111 for further reference.
This appears intended and is not restricted to multiplayer. Hold shift to go down faster, if this is what you are referring to.