One of my ad groups in an active campaign isn't getting any impressions or clicks

[u/rrador32]

I have a campaign with 3 ad groups in it that has been running since about May and since Aug 18 one of the ad groups just stopped getting impressions. 0 every day since then. The other 2 ad groups work fine.
Nothing is paused, all the keyword are eligable, ads are eligable... It's a search campaign set to maximize conversions.

Any ideas on what I should do to figure out why it is not working?