Dramatic engagement drop

Long story short, I had an instagram account with 20k followers on my own. Then I got a bot and did likes and follow/unfollow for a while, and got to 40k followers.

Everything was great, my engagement was like 5k likes per photo with 100 comments.

then suddenly a few days ago, my photos would get like 100 likes & 4 comments.

I read about shadow banning, and though i never use hashtags on my photos, i tested it, and my photo does come up in the hashtag searches even if I check from a different device.

But what the heck happened to my engagement? I stopped botting for a 4 days, but it still hasnt returned to normal yet.

Any advice? Should I wait a little while longer?

Dunno but its not shadowbanning on the hashtag. IG has probably flagged your account and only showing your posts to 10 percent of your followers. They have the ability to throttle reach.
This happened to me on a few accounts last year and it never recovered.
You can try this method by tux, it might help claw back some engagement. https://www.blackhatworld.com/seo/method-recover-your-engagement-on-instagram.959849/
Maybe it will come back on its own. Just rest the account for a day or two then post again, see how it goes.