check if pH is drifting in soil -- slurry and ph meter... won't tell you exact pH, will only tell you direction it is going from intial solutions pH before slurry. So, if it drops or rises drastically, this may be cause.
looks like a trace element, and that's rarely a problem, but pH can lock something out easily even if it is 'there'.
if this is what you used in other diary, looks a bit hot... lines up with lockout guess.
interveinal with soem spots... Mg is also on the board here. If you eliminate other possibilities, some epsom salt would help here. how much depends on what is in yur nutes already... what the soil has etc.. so you'll hve to guess and fill in blanks if it come to tht.