Are you priming the keg? Or do you prime the bottles separately?
I prime the bottles individually with dry sugar. This is immediately after racking to the keg, before it starts to carbonate.
Perhaps a final question, since we're off topic...
Are you weighing out corn or table sugar? Or do you use one of the various carb tabs?
If you weigh out sugar, how much per bottle?
I'm not a big fan of the carb tabs, other than they're super convenient.
In reality you are much better off bulk priming at a rate of .75-1oz per finished gallon of beer.
Add priming sugar to 1 cup boiling water to dissolve, add syrup to bottling bucket and rack beer onto it. The swirl will mix the syrup in and then bottle.
This method will give you the most consistent carbonation throughout the batch.
Priming by individual bottle can cause mixed results of over/under carbonation. The weight I provided will get about 2.3-2.5 vols of CO2