Hi Tom,
I have had similar experiences with lockouts with several autopot grows and have done alot of research and headscrathing. Some of my findings/experiences were. Firstly, it never happens to all the plants. It's just one plant. And I have learned to catch it early and resolve it by flushing that one plant. I usually grow 2,3 or 4 plants of all different genetics per grow. So,I thought it might be genetically related with that plant being sensitive to the ppm of the nutes that the other plants could tolerate. Another observation---It usually happens to just one plant. One time I thought it was related to turning on the reservoir to soon for one plant. One time I found, again with one plant the valve was semi stuck leaving the tray rather full and therefore not getting that dry tray cycling.
The next "tear" im on is---I'm fiddly fucking with is the coco itself. This next run i am doing a heavy precharge of calmag and soaking the pot for 12 -24 hours, based on some well written research and also strains the small pieces of coco...since my bagged coco is cheap and have no clue how to contact the company to see if/how it was treated. I am also reusing coco from one of my past grows pretreating it the same way.
For what it's worth, I have seen a grow or two that had lockout even though they used airdomes.
I would say screw it and not use the autopots, but they are so handy and a necessity when I have to travel. It baffles me to since if it was salt build up I would it would happen to all the plants on that particular run.
Which leads me to think its one fussy valve related. So, also will be checking the valves daily this next run.
@St. Tom .
I don't want to bombard you with research articles. But, if you are interested----here is a decent article(s) for coco knowledge.
Peace, and love your grows!