Insiders tell THR that “very protective” comic book writer Robert Kirkman was one of many who clashed with now-fired Glen Mazzara.

Also…

One source says Mazzara’s shortcomings in running the series during the most recent third season became “abundantly clear … especially for the second half of the season.” This source says production was shut down “several times” because of a lack of material. 

Good news, bad news I guess.

Regardless, AMC has a real showrunner problem.