New Website Skyrocketed at First, Then Crashed. What's Going On?

A few weeks ago I bought an 11 years old domain, with some very good backlinks and DA47.

I installed WP on it and tried to reconstruct old posts that receive most of backlinks. My writers came up with articles that mimic old posts, so strongest backlinks now don't point to 404 error page, but to reconstructed posts.

The old website had a forum and forum members created lots of backlinks to their profiles on other sites. Since I can't recreate those old forum profiles on my domain, I redirected them 301 to the homepage. Not sure if this was a good idea? (example: yoursite.com/forum/profile/sad-raccoon redirect 301 to yoursite.com)

Then I posted 20-30 fresh posts and my traffic from Google skyrocketed from 0 to 500 in 2-3 days. Everything I posted was ranked in the top 10-20 on Google as soon as Google indexed it. Life was good and I had bright hopes for the future.

But just a few days after that my rankings started to drop and a few hours ago I noticed that I cant find most of my posts in SERP or they're stuck at the position 100 or so.

Not sure if I was just lucky to get all that traffic at first or I just screw up something?

A few days ago I received an email from a very popular Youtuber, he noticed that one of my writers turned one of his videos to an article and screenshotted his video to make images for the post. He didn't say that he's going to report me or anything like that, but maybe he reported me to Google? I never replied to his email, btw.

My content isn't top-notch, I know, but still, it's not the worst on the net. I'm using $5-$10 articles. Guys that write it just read a few articles on the topic and then write their own. Each article is 100% free of copied content. Not fantastic content that "adds value" and provide "great experience", but its much better than lots of articles on the second and third page of Google.

Not sure if I'm inpatient, it all happened in just less than 10 days, or I screw up something? What could it be?

that's normal
it's google dance , so the website should go up ad down before it stick to a position

@majdi107

You really think I'm not penalized or anything like that? I didn't receive a manual penalty, but...

One thing I noticed as well... when I search in Google for my posts about "best strategy games" my post about that topic doesn't appear in search results, but my another, random post like "what games to play during vacation" appears instead (on the position 50 or so). That tells me that Google still doesn't understand my site well and looks at where to rank my pages.

Since 2016 when Google massacred my 7 great websites I had very little success. Not sure how many more defeats I'll be able to survive.

Just checked a page that performed well. It was on position 6 when it was indexed for the first time, now I can't find it in the top 100. Instead of it, there are two of my other posts. When I do site:mywebsite.com search in Google I don't see that post in the list of indexed pages/posts, but it is cached by Google. I published it just a few days ago. Is this normal?