I've seen this quite a few times. In most cases, there is a grounding issue near your cable equipment. Obviously, A/C will search for the best ground, and in these cases, it's the coax via CPE. When you check for MER/BER issues with your meter, you will never see it because you have broken the loop when you disconnected the coax. Whenever I'm on a trouble call and see the word "intermittent", that's actually one of the first things I check for. I disco from the GB and put my red lead on the stinger, black lead on the ground wire. If there's voltage coming back, I see it. Just make sure you're using an RMS multimeter. Any other cheap multimeter will give you false readings.
This is CABL.com posting #359338. Tiny Link: cabl.co/mbFDW