The site fell in the search and does not rise, how to find the reason?

Question

Search Engine Optimization

Hello!
Please help me figure out what I'm doing wrong with website promotion.
The site occupied the middle of the first page in Google search for low-frequency queries, now it has moved to the second page and does not return to the first (within a month).
All title and description are filled in, google page speed is in the green area. Self written in php.
Once a week I buy a link to a promoted page that has fallen in the search. The quality of sites I choose is something like prntscr.com/ocyd2u. Links are either thematic, medical, or regional guides.
About once every 10 days we add a unique article, and we also buy a link for it. The quality of the sites is: prntscr.com/ocydkf. Articles are indexed, there are no problems.
Errors that are currently not fixed on the site:
1. Windows-1251 encoding, not utf-8
2. Several errors (about 5) in the validator
How much can these errors affect promotion? Competitors have much more errors on their sites
. Also, in terms of the number of links, on my site so far the link mass is about half that on the site of competitors.
They took a break in the publication of articles for three months, could this have affected?
Please tell me what to pay attention to and what to do in the first place, I will be grateful for any ideas

Answer 1

Means not such good links were.
And if you use the new google search console, then look at the new one, there are messages there.

Answer 2

Google loves fast websites. up to 200 ms. you have 15 times more.
The picture in the assessment hurts the eye by almost a meter and a half.
Purchased links in my opinion have been working in the negative for 4 years.
The theme of the site is the same. Yes, and Central Asia is only one million-plus city.
And the phones that affect the regional binding are placed with a picture.