I'm about 100% sure when you pull the plants youre going to find a lot of rotten roots, especially near the drain end. I had the same issue with a similar setup, roots looked solid until about 4 weeks then they started failing cause theres too much stagnant water. They're also probably clogging your drain line and slowing the ability of the water to run out, making the rot issue worse. You can upsize the drain but it doesnt make a lot of difference as soon as the roots start growing into it they will constrict it regardless of size. The only solution I found was to leave the ends open and use a trough style drain like SuperStoner's setup. I got tired of the leaks and ditch aero in favor of ebb and flow. Maintenance is zero. I've been gone 3 weeks and system is running fine with no adjustments and only a small top-off. I'll post updated pics tomorrow.