About every three months I have to "de-scale" my Keurig K-Cup pot when it starts dispensing a partial cup... even though I use R-O water.
Three months ago I went thru all the clean with vinegar and flush routines and it still dispensed partial cups.
Repeated all the recommended operations, still wouldn't work.
Pondering the way the reservoir was made with a check-valve at the bottom, I wondered if that was the problem.
Took it outside, applied the garden hose to the valve, from the bottom, made it "whistle" >:-}
Returned it to the pot... problem gone, worked fine.
Yesterday, partial cups :-(
Applied the garden hose, problem solved ;-)
Try it next time your Keurig pot acts up. ...Jim Thompson