Homepage Rankings/Traffic Completely Tanked - Help!

Hi, all. Very strange - homepage traffic on a non-profit site dropped suddenly with no real explanation. Ran the site through tools such as SEMrush and Ahrefs and not seeing any errors on the page, it is not blocked by Robots.txt, etc.

Any ideas as to what else I should look at? I do know they had about 80 domains pointing to the site and then it went down to 16, so they said they did a "server-side permanent" redirect of all of these domains to this homepage. (non of these domains ever had content on them or were ever ranking themselves)

Assuming something happened here? Any tips, thoughts of where else to look would help greatly.

Trying to insert an image to show you GSC so you may see how crazy this is.

Thanks in advance!

-Jes