Are the plates and knives sharp?
Dull knives will grind slow and cause things to warm up.
Does the drive end of the auger (back end) have a fiber washer where it contacts the grinder housing?
That was going to be my suggestion. He could start by buying a sharpening stone and resharpening the plates and cutter. If that does not work then that may be a good opportunity to UPGRADE LOL!!!
I don’t mean to derail the main topic, but what you want to sharpen your own grinder knives and plates is an absolutely flat surface abrasive. Unless unusually large, a sharpening stone will not have the size and flatness you need.
What works well for grinder plates and knives is a flat counter top with a sheet of wet/dry silicon carbide abrasive paper, about 400 grit.
Lay the sheet of abrasive paper down flat on the counter and just work the grinder plate in a circular pattern on the paper till you get a uniform smooth polish on the plate and have removed all knife wear patterns from it. Use the same process for the grinder knife.
This works for plates/knives with light to moderate wear. It won’t work that well for stainless or disposable knives and plates.
I have never used the grinding stones that the sausage maker sells but I thought it was a good concept. Eric at 2 Guys and a Cooler seems to advocate for them (but let’s face it he is sponsored by them) but I believe I have seen another video where he did what you mentioned with the sandpaper.
I looked that the stones sold by TSM and watched the video.
For those not familiar with them, the stones are round and fit inside your grinder head with the plate or the knife, depending which you want to sharpen.
When the auger turns it rotates the knife against the stone and puts a fresh edge on the knife.
The second stone rotates the stone against the stationary grinder plate.
I have not used this product but I would have some reservations. Using them in an electric grinder looks like it would be easy to break the stones if you were not extremely careful adjusting the grinder head nut.
Over time, the stone for the plate is also going to cut a groove in your grinder plates because it is smaller than the plate is.