Got hit myself a month back, April 1st went from 300k/48hrs to 20k/48hrs, up to around 60 now but not a single suggested view to new videos. Don't really know, waiting on internal review but have been waiting for a month now and they are seriously really slow.
I can tell you this. I did my fair research and from what I can tell this is happening all over the place. Many channels who I've tracked for years and they usually did 20mil views/vid at average and have 4-5m subs. They now have an average of barely 1m on their new uploads.
I am hoping shit settles down, but still no luck with suggested views. Shadowbanning is just lame. Tell people what they do wrong so they can adapt instead... I mean I spend 20h per video and my latest barely got 200 views first day down from my regular 50-100k first day.
I've taken the time to send some card traffic to 3 new channels to get them up to 1k subs and monetize. I mean with 3 others you might have 1 pushing on while the others fall and vice versa
Learn the importance to diversify. I get shot down at least once a year and the first few years I fell down to almost 0$. Now I can survive a couple of months due to savings when times are good. Don't wait and stall, start something new while still pushing to see if your last channel will get back to normal soon.
Then a question for my own curiosity. Are you also 100% out of suggested views? Check your latest videos. I get some for one of my old videos but barely noticeable. If you have found anything else that could be interesting to know feel free to share.
Heres a link to my post if you want to read some more. I'll keep on updating it when new things happen:
https://www.blackhatworld.com/seo/views-hr-drop-from-350-day-to-25-in-1-hr.1108818/
I've been uploading 3-4 videos a month too so I don't think it is for spamming.