Same issue - PC Steam.
My save prior to the update had Natural Explorer enabled. I didnt notice any run speed issues prior to combat, killed a weevil right after loading, and turning off natural explorer, the run speed is extremely slow. With the mutation on, run speed seems about normal run speed should be with no buff.
Killed a bunch of weevils and it was extremely slow. Tried loading the save on a couple different PCs, but the issue was the same.
I ended up killing a few more mobs (something that I couldnt 1 shot like a weevil), killed a red soldier ant, and then the run speed seemed to fix itself again. Seems like being out of combat does not register on mobs that you can 1 shot or kill too quickly.
Once the run speed seemed to be corrected, I went back and killed a weevil and it was super slow again.