Why is it taking so long to film a season?

A three-season series has been stretched out over years. Why? This isn't "Dragon's House" with costumes, battles, and CGI. This isn't "Fallout" with its fancy makeup, mechanical special effects, and numerous locations.

This is a show where the locations are a forest and three barns. And where infected rarely appear in the background. Like "The Walking Dead," they filmed 20 episodes a year.