Also sometimes happens when hacking magma blocks away when standing on top or at the side. There is no sound like leaving/entering water, the ambience is still underwater but no drowning.
They sometimes begin to race in circles and die with apparently no outer cause.
I have the same issue like the tools are all on a kind of auto fire. Does not happen with other items or fists.
Please vote for this issue in the right upper corner of this screen, so it gets attention from developers.
Even walking up stairblocks is affected by this. No smoothly walking up a staircase. Movement "stutters". Also "Auto-jump" on or off does not have an effect on this behavior.