Solve Error 520 (Web server is returning an unknown error)

Hi,

I purchased a VPS server from a hosting company and things were good, but after a while, “Error 520” appeared, and this error does not appear continuously, but intermittently, especially when opening many pages of the site, and in the dashboard when adding or modifying topics. Usually, refreshing the page once or twice is sufficient to solve the problem.

I contacted the hosting company and they told me it was not because of them but from Cloudflare, I contacted Cloudflare and the result was the same.

The hosting company confirms that the server settings are great, and Cloudflare confirms that the problem is not theirs.

Want someone to fix this problem?