That's a calcium deficiency.
Most DEFINATELY so.
I suffer the same spots in my own grow and often find I'm adding copious amounts of extra Ca to rectify it.
Generally what I do is feed with my normal mixture and then make up a second mixture with mono Ca and mono Mg and each plant showing the spots gets an extra litre of the Ca and Mg mix.
Generally I feed the Ca and Mg at almost full strength to treat a deficiency 1-2ml per litre.
In 5 litres I'm adding 10ml mono Ca @11% and 5ml mono Mg @7% and this gives me an EC1.4 about 1000ppm @.7 scale.
I do this anytime I see the spots.
Generally after 3 feeds like this the spots stop.
Anytime they reappear I redo the same mixture.
J