I think it’s time to just call it a bug and report it as a bug, which I’ve done here: Command table "Maw" missions bugged.
I’ve had all my original followers at level 60 on the mission board since around the time the patch dropped a couple weeks ago. I’ve still never seen any “Maw” mission other than the initial four for the achievement.
I’ve read the wowhead comments, and come across comments here and there about it elsewhere. Sure, a rare few people have had it continue on. There’s no consistency to what makes it happen, and brushing it off as, “well, it’s just RNG” means they intended for this series of missions to have some ridiculous spike in unavailability after you get done with the first 3-4.
I don’t think it’s just RNG. Especially since early on, the missions would just follow one week after the other, and the versions of the missions that have the word “Maw:” in it never repeats (indicating that the intended design was probably for us to get the next one in the chain the week following a successful completion of the prior one).
I think something in the command table algorithm for this series of missions is broken. Once every very rare while some person might get past whatever’s broken about it, but this functionality just seems too ridiculous to be intended.