Distance WAY too low when walking on Treadmill

Hey all, Apologies for the potential repeat post but I've searched a lot and haven't found quite the same issue.

I walk 20,000 steps on a treadmill almost every day. Only recently I started actively trying to lose weight again, so I'm checking my distance and calories burned.

Typically, 20,000 steps would be in the 15-16km range, but lately after 20,000 steps I'm getting like 5km, which is wayyyyy too low, and really affecting my calorie bonus as well.

I've tried restarting the fitbit, factory resetting it, disconnecting and reconnecting it from the app, wearing it in a different spot on my arm, changing stride length etc.

My stride length is set to 78cm, and it's tracking steps accurately, so I have no idea what's going on. Any ideas?

**EDIT: For anyone who ever sees this with a similar problem. I think I figured it out! tl;dr: Put it in your pocket.**

I use a treadmill desk so my arm doesn't sway a lot while walking. For some reason the lack of arm motion would still count steps accurately, but wouldn't count distance or calories anywhere near as high as they should be. I put the fitbit in my pocket while walking and now it tracks all three metrics accurately. Not ideal, and something still seems wrong with that, but at least there's a workaround.