Thanks for the replies, guys.
It sure does look like it.
I have cal-mag added to my soil at 1kg/m3, magnesium 154mg/l.
That should give me a moderate Mg level, from what I gather.
But Cannabis seems to be a heavy Mg feeder, so maybe just needs more.
I guess it could also be due to a problem accessing the Mg in the soil.
humidity is stable around 50RH and temps never go under 18c.
PH might be too low? My soil is supposed to be at 5.5-6.5, growing organic so figured it should stabilize itself.
Thinking of giving some foliar spray with epsom salt. What do you think?