I used to have that happen when I would overfeed way too much, TDS well into the 4000s. Another thing could be the water isn’t moving enough to keep everything mixed, or your adding nutes too close together.
Depending on your air pump and stone setup your water might not be moving enough to keep the nutes from binding with each other. For example I run 2x 10" air stones with a 4w airpump for each of my buckets. This is about the lowest amount of air I get can get away with and not have issues with mixing.
Also when I mix I leave between 15-30 minutes between bottles of food (micro, gro, bloom) Not as much time between support nutes (floralucious, flora nectar, diamond nectar, etc…). Things like armor si and calmag i add a day or so off schedule from the main feeding.
But mostly I think it was reducing the ppm theses days I max out in bloom around 1500ppm. And I don’t flush unless I run into a issue.
Another thought I way back when I started I tried pre mixing in a small 20oz bottle and found that was a great way to combine my nutes into sludge. Now if premix in flower ill do it in a few gallons of water, but that is only when go out of town for more than a week.