Please call our tech team at 1-888-411-5282 ext 3. I have an idea what it could be, but they will know best. Which is strange because your issue is very rare.
The total amount of coffee that ends up in the cup is very inconsistant, with a 2-3 oz variation. I've tried priming and cleaning. We've had the machine for about 5 months and it ran perfectly for the first 4 months.