What sounds to be happening here is an issue caused by the event fast-forwarding feature in RMMV (I think it only applies to playtesting, but don't quote me on that). When an event is in motion - in this case, when a region tile is stepped on - if the action button (left mouse button, 'z', et cetera) is pressed down, the event process will be fast-forwarded. Since each step within that region is an event, it is a continual process.
I don't think that's the case since it only happens with the mouse, infact, I cant even trigger the event with Z on the keyboard. Also, I tried it in a deployment and still get the same bug.
Edit: Nevermind, I see what you're talking about. Guess I'll try looking for a plugin to disable that feature and see if it solves the problem.
Edit2: Well that seems to have solved the problem with the game speed. However, the sound looping issue is still there. Unless there's something else I'm overlooking, I'll try suggesting that Yanfly include an option to disable triggering an event with a mouse click, so that it'd only trigger when stepped on.
@MasterTaffer I use Region Events as well for step sounds. Additonally, I use a plugin from SumRndmDde that has the option to wait for completion for sound effects.
I still get the same exact problem with that script, so you might want to check your own game for this bug.
Edit: I tried it again with the fast-fowarding feature disabled, and now I'm getting some bad stuttery movement - not sure if it's just my computer (doubt it) or what. Before, I just set a switch to toggle on and off after every step, so the footstep sounds would play every other tile (note that dash is disabled for my game).