The answer is yes, there are a few random spawn locations where Abadon Crusher Mutants may spawn.
The first location is in southeast of the town 'Gunbarrel' in a meteorite craters. The second random spawn location is in the southwest of the town 'Wellspring'.
I found (later) a third random spawn location. Directly above from the first MBTV location in Broken Tract.
No, you're not done yet but you have to complete the quest lines for Marshall and Loosum also.
EDIT
You're over level 5 with all of them and assuming you have no quests left for any then this may be a bug as reported by many other players. Some people got it moving by reinstalling, some people by fast travelling.
Best Answer
Abbadon Crusher mutants are all unique bosses with different weak spots.
This list is sourced from GamesHedge
Lug the Nut’s weak point is the head
Smeggle The Vile’s weak point is the chest
Sackhead’s weak point is the back
Digg and Dugg don’t have a weak point - but the arena is easily accessible by vehicle making for a fair fight
Grull the Juggernaut’s weak point is the unarmored legs
Generic abbadon mutants can spawn in a crater south of Gunbarrel too. These don’t seem to have a weak point but can again be fought by vehicle