You are in soil so your PH should be much more alkaline, 6.5 as a base 5.9 is low low.
Plants are different some will be fine with that PH in soil but now this one.
CA, Mag, Phos all start to fall off below 6.1 in soil.
Just my opinion
Pretty good, just a few more days of patience. Let the comfrey dry in the sun, then crush it and put it on the soil to finish until the harvest. A friend does it.