Is this a trackable environment? Screen names and Databases in play? If it is, I would have a note on you and I would be flatting you often IP with the big pairs and letting you barrel off. I would be less incentivized to 4b for value with nutted pairs. Basically, I would use your barreling strategy against you and deal with the consequences the times you out flop me. This could be the culprit as to whey you feel it is happening over and over again.

Vs anonymous pool, I mostly range bet OOP in 3b pots. JJ is squarely in my betting range. I will size down some. Any bet puts pressure on the unpaired/no draw portion of his range. Basically if I discovered the leak, I would begin to experiment with some alternate lines. I might even consider betting smaller with the 99-JJ/QQ range and betting bigger with the KK/AA/Trips/high equity bluffs. I might even experiment using another small size on some turns.

Have you run a filter with the hands in question and set the filter for HU 3 barrel? I am sure there are spots where you took this line and got called down by underpairs to your holding and won some big pots. Also, sample size is going to play a big part here. You could just be running into the tops of ranges over a smaller sample also.

x/c turn if villain floats, x/f turn if villain doesnt

River bet will be thin when villain's are tight and they don't hold many 8x combinations and even when they do they might not be willing to pay 3 streets. So you need to check somewhere turn or river and once facing a bet act accordingly to their range and potodds received

You have to ask yourself what are you trying to get called by and the amounts of bluffcatchers villain has and will call with vs the hands that have you beat decides if its a valuebet or not

99,TT and JJ very different hands and different vs MP/CO and 2.5x/3x. Plenty of variables

Likely your opponents overfolding somewhere and that leads to cutting 3street betting strategy. (Feels like they fold often PRE, and flop. So on the river they arrive with pretty thin range: vs those folding river after checking 100% might be solid approach)