I believe the "sugar didn't mix properly" idea is a bunch of hooey. I subscribe to the notion that two tiny cups worth of priming solution dissolves itself just fine without the need to stir when placed in the bottling bucket and the 5 gallons of beer is racked on top. When the 5 gallons starts swirling and lifting up the bucket it mixes itself just fine.
And that inconsistent carbonation is merely impatience. Some folks feel the need to stir, if it makes them happy fine. But I'm more concerned about oxygentation and possible infection risk....And my experience has been that the sugar solution mixes itself fine on it's own.
The
3 weeks at 70 degrees, that we recommend is the
minimum time it takes for average gravity beers to carbonate and condition. Higher grav beers take longer.
Stouts and porters have taken me between 6 and 8 weeks to carb up..
I have a 1.090 Belgian strong that took three months to carb up.
Temp and gravity are the two factors that contribute to the time it takes to carb beer. But if a beer's not ready yet, or seems low carbed, and you added the right amount of sugar to it, then it's not stalled,
it's just not time yet.
Everything you need to know about carbing and conditioning, can be found here
Of Patience and Bottle Conditioning. With emphasis on the word,
"patience."
If a beer isn't carbed by "x number of weeks" you just have to give them more time. If you added your sugar, then the beer will carb up eventually, it's really a foolroof process. All beers will carb up eventually. A lot of new brewers think they have to "troubleshoot" a bottling issue, when there really is none, the beer knows how to carb itself. In fact if you run beersmiths carbing calculator, some lower grav beers don't even require additional sugar to reach their minimum level of carbonation. Just time.
Give it a couple weeks and I betcha they will be carbed just fine. Each one is it's own little microcosm, and although generally the should come up at the same time, it's not an automatic switch, and they all pop on.
But they all will pop on when the time is right.