Mystery for me is still your EC/pH values. When you go out EC 2,6 your pH will be likely below 6,0. Measuring your runoff by the sides of the pot is useless. You need to add water in the midlle very slowly to avoid this side running and wait untill you get 10% runoff and than measure! If you got less only for measurement your readings will be inaccurate. For example I need to water 4 litres to get 0,4 runoff, when I water 3,5 litres I get only 0,1 runoff and this tell me nothing about the real values. When yours first 10% runoff is too high of EC, than you need another 10% (not mixed with the previous 10%) but ofc you will need much less water than for the first 10% but you still need 0,4 litres runoff (in my case) to get the sample for measurment. The highest concetration of salts is in the last “drops” and it has a big influence to the overall results. And why to feed them after flush? Because they are locked out of nuts, when you perform flush correctly, you should ended up with very low amount of them in your soil plus your plant is suffering but should be able to uptake already, but when there are no nuts, deficiencies go on further...