This is just my opinion, so don't shoot me!
I had the same problem with a kegged Belgian Golden Strong Ale. Tried to get higher than normal carbonation, as called for by the style guidelines. But, when I poured the beer, I had the perfect moment to insert the ole trombone "whaa-whaa-whaa" sound...as in "no bubbles for you, sad sack.
What I later figured out is that I was serving the beer too cold. It was around 40 F...seems it kept the CO2 from effervescing...so no bubbles and flat on the palate. I brought the temperature up to 48, and started getting bubbles the next day; I also got more aroma and flavors.
I latered noticed the same effect when judging at a competition; really cold entries showed no signs of carbonation.
You could try this: get a bottle -- either cap-able or swingtop -- and chill it. Disconnect your CO2 cylinder and vent the keg until you have just enough pressure to s-l-o-w-l-y dispense beer into your chilled bottle, fill the bottle the the very top and cap or engage swign top.
Then either let the bottle slowly warm up to around 50 F, or store for a day in a fridge that stays in the high 40s. Then open and pour to see what you get bubble-wise.
I just think there must be a correlation between a beer's serving temperature and it's expression of carbonation. Too cold, seems flat; too warm, seems gushy.