Nutrient lockout or deficiency

if this is a soilless grow and you are not regularly getting 10% runoff waste water, you likely have a buildup occurring in the substrate. that waste water if fine outside but not for potted plants. don't let it sit in its piss either. Runoff should be higher, that is expected, but 3.5EC is probably too high. The small amount of runoff may have been a big reason for how high it was, too. Regarardless, i'd dial back a bit on nutes. You don't have to 'flush' unless it starts progressing very fast, otherwise take a measured approach. Maybe just 1 water-only irrigation with 10% runoff then back to regular fertigation. Be religious about that 10% runoff. It's very important, if in a soilless context with "hydro" nutrients. give a wide berth, but anything WAY off from these numbers is a potential for buildup over time. PPMs N 120 P 50 K 190 Ca 100+ Mg 75ish S 100-110 possibly more? Your local tap water as well as average VPD will impact these numbers too. Should be solid for anything 5.8-6.2 pH and probably even wider range than that. Anything more than 20% different, i'd reference a leaf symptom chart to see if any of the leaf symptoms you see match up to the ones that stick out due to ppms. That's only for a soilless/hydro context and not a substrate that provides nutrients in addition to fertigation.