Was about to start my own thread but this is somewhat similar to what i'm having. I'm thinking either cal/mag deficiency or fungus, but since i grow in a small closet with an exhaust fan constantly running, i'm not sure about the latter. Started showing about a week after replanting (solo cup to 3/4gal pots), first on one plant (first 3 photos, it's the one on the top right), now others are showing symptoms.
Watered the plants today, after a few days break, just took a moisture reading of 45. Label on the soil pack says PH 6.5, also said to contain ground lime with MG content. Still need to wait a couple days for calibration fluids to get a confirmed reading.