Looks like you're getting good advice so far.

You need to gently slide the plant(s) out of the pots and have a gander at those roots. That's one good thing about those tapered square pots; they make that easy. Use a "frosting knife" to loosen things up if necessary.

If they're rootbound, it would explain your apparent N deficiency symptoms. Adding more N won't help if you've got a lockout. (A flush followed by a light feeding usually temporarily improves lockout symptoms, so you could try that with a plant or two as a diagnostic tool...but you'll still have to deal with the cause.)

If they look rootbound, they'll need potting up, but IMO only to the next larger available size. Repotting won't stress them, they'll love it if they need it. But most strains I've worked with lately haven't generated much new root growth after the 12/12 flip. That's why I'd advise a pot size increase of only 1 increment. Plants at this growth stage may not drink a 5 Gal container dry enough between waterings, and sloppy soil will give you a similar-looking set of problems.