It's because of a bug we had that made credits disappear when they were added to the season while they were already added to an episode on that season. I just took care of this one, David Lynch should show up as a Director on your API call once the cache clears.

Thanks a lot for the fix!

I found a similar case. Although Issa López is credited as "director" for all episodes of the 4th season of True Detective, the https://api.themoviedb.org/3/tv/46648/season/4/aggregate_credits? endpoint gives no "director" at all. Is this also a bug or is this intentional? I assume it's not intentional which brings me to the question: Is the forum here the right place to address issues like these? Or what else should I do? At least it looks like I can't fix it myself.

Yeah, that seems like it's a bug with the aggregation on a seasonal level, I only see regulars on this page too: https://www.themoviedb.org/tv/46648-true-detective/season/4/cast, though https://www.themoviedb.org/tv/46648-true-detective/season/3/cast does show everyone in season 3 properly.

Is the forum here the right place to address issues like these? Or what else should I do? At least it looks like I can't fix it myself.

It is, yeah! I've also gone ahead and reported it internally.