Yeah, that’s a mess all right. 
If you can see visible gunk on the belt, there are instructions here for how to remove the Carriage Plate and remove the belt for cleaning or replacement. I would wait to hear from Support that you should try to do that though, they might see something else causing it. Looks like it might be a bit tricky to reinstall.
Before you do that, you might want to check the condition of a few other things for buildup:
- Check the bottom of the Print Head - there are two small windows on either side of the lens opening that need to be kept very clean. If they are dirty or obscured, clean them with a Zeiss wipe and see if things improve.
- There is a little fan in the Print Head on the back - that one needs to be checked to see if it is clean or has a lot of buildup on it.
- There is a larger fan on the Carriage Plate. That one should also be checked for buildup of crud. (Look down behind the gantry with a flashlight to see it if you don’t want to take it out.)
- Check the condition of the Exhaust fan at the rear left of the machine while you are at it.
If either of those front fans has a lot of buildup, it’s going to hamper the air flow that keeps buildup from happening in the first place, and since you do a lot of heavy engraving on resinous materials, you are probably going to have to clean them on a regular basis. (Looks like more than once a month based on your usage.)
Canned air and vacuuming will not remove resin buildup. That has to be wiped off. It’s sticky and gets almost baked on. I have instructions for how I cleaned the exhaust fan here, and it’s not a Glowforge approved process, but it worked. I use the same process on the head fan and carriage plate fan, without removing them from position, and it keeps everything blowing the way it’s supposed to.
For cleaning under the gantry, I would try this:
- Unplug the machine.
- Take off the Print Head and carefully set it aside. (Check the bottom for buildup and look at the fan on the back. Clean anything that needs cleaning. Zeiss wipes for the windows and lenses.)
- Get a small rag or paper towels and a bunch of Q-tips for detailing. Mix up a 50/50 vinegar/water mixture. Dip the towel in the solution, wring it out so that it is moist, not wet, and start carefully wiping the gantry down. Top, underneath, back…whatever you can reach with the rag. It removes the resin buildup better than anything I’ve found, and I use it on everything except the electronics. Use the Q-tips around the wheels, or anyplace you can’t reach with your hand. And try not to use too much liquid.
Use a mirror and flashlight to see what you’re doing…I’ll bet you can get most of the resin buildup off of the gantry itself.
And let it dry overnight with the lid up to make sure there’s no liquid left in there before you fire it back up again.
Since the woods you are burning are what is causing the resin buildup, you might want to switch to a less resinous wood to keep from having to clean so often. Unfortunately, heavy engraving seems to cause faster buildup than cutting, and I usually clean everything (tube, bed, gantry, tracks) after a heavy engraving session. If you don’t let it build up, it’s easier and quicker to just give it a quick wipe down and it’s good to go.
Hopefully it just needs a little cleaning and you’ll be ready to hit it again. 
