So basically, Ive experienced this under two circumstances. When carrying many packages between servers, I became unable to run and had to log in and out, use detect and stealth mode to no avail, until randomly I could run again. The same goes for becoming encumbered. When I become encumbered, even if my weight changes, I can no longer run. Usually logging fixes it, but after buffing my strength, relogging is not fixing it. So, I am currently stuck walking on Arelith.
Just to be perfectly clear that yes, I did in-fact check my weight and buffed it, too
Edit: After many log ins and logging out, trying toggling alwayswalk, detect mode, stealth mode, randomly after a bunch of logins, I tried toggling alwayswalk on and off again and that fixed my running.