That in-pot pH reading is what will determine the next step,... we don't know if it's still too high in there, or if this is simply lack-of now with such mild dosing,.. could be that this is just a sickly plant, which is anything but uncommon! I have had some that were bitchy about micronutes their whole lives, usually inferior performance/results too....
Tap water at 7.3 doesn't sound very hard, shouldn't drive pH up like that... but only a TDS/EC reading can solve that,...
you can try the flush, but if you do take readings of pH and TDS of run-off at beginning, middle and end, best you can estimate, to see what's going on there,.. If the first run-off is OK for pH/ppm, you don't need to do any more,... it's not a reliable measure of actual in-pot pH, but a crude estimate.. be sure to use unadjusted water, RO/Di/very low ppm water is important here, tap will have minerals in it that buffer pH and so will skew results.... BB nutes are mild, mostly organic, so pHadjusting the feeds and flushing are usually not recommended....