Wait, are you asking why your beers are inconsistently carbonated or why they have a chalky taste to them?
If you poured your carbonating sugar in one area and didn't stir it around, I believe that might be a problem. I've heard it likes to settle at the bottom, so some of your beers can be too carbonated, while others aren't carbonated enough.
The chalky taste may be attributed to your water, more specifically, the calcium carbonate content of your water. you may want to get a water report, or at least check the CaCO3 reading.