You are probably getting an air lock under the machine surface or base plate. Drill a small hole in the base plate, inject the grout from another location, and if you can, pull a small vacuum on the drilled hole. This will help you remove the air lock. If you can't pull a vacuum on it, at least make sure it stays open as the grout is put in. You can pull an adequate vacuum with just a small hose and a little reverse lung power. Be careful not to ingest any of the grout! Also, you might need more than one hole. You will need the vacuum on each hole simultaneously.
The air lock is probably a result of a warped or non-flat mounting or base plate.
Good luck.