Low humidity isn't a factor when incubating BRF jars or grain spawn. Not usually, that is. If they stall for some other reason (see below) and sit around for a lot longer than they otherwise would then it might become an issue.
There's a chance that they might be getting dried out if they're too close to a heat source they can "see" (you don't want there to be a direct line of sight between a heat source and your jars or bins). Radiant heat drives the moisture out much faster than it would normally evaporate, and the total lack of condensation on your jars suggests that this might be what's happening instead of or in addition to a lack of gas exchange.
If they are not getting any gas exchange at all then that would definitely cause them to stall like jrh mentioned. So it's possible there are two issues (lack of gas exchange and drying out due to radiant heat). Also, 79+ degrees is a bit too warm. Try to keep them at 75, 76 max (for both incubating and fruiting).
The growth in your popcorn jar is gorgeous, by the way.
A shake would help them finish up quicker, assuming the stalling problem can be fixed. Sometimes a jar that looks great will contaminate after a shake, but this is not caused by the shake (the contam was already in there, just not detectable yet) and if that happens just think of it as sparing you the time, energy, and effort that would otherwise have been wasted if you'd used it to spawn a bulk sub.
I always shake up my grain spawn the night before spawning it to bulk both to reveal any hidden contams and to give it a head start in recovering from getting all torn apart.