The server host is limiting the site performance, saying it is caused by slow queries, then pointing to wpForo as the cause.

This is from a chat with the host:

The forum is not just slow for one visitor. The logs show a repeated pattern:

• Many GET /forum/ requests take approximately 16–83 minutes to finish.
• Several end with HTTP 500 after roughly 45–86 minutes.
• Other requests return HTTP 200 but still take an abnormally long time.
• Bingbot requests are also hitting /forum/; several were rate-limited with HTTP 429.

That means the forum page is triggering a long-running WordPress operation. The most likely sources are the forum plugin itself, its database queries, or an attached feature such as Better Messages, not the basic hosting connection and not your SELECT 1 test.

The access logs cannot reveal the exact SQL statement or plugin function, but they do establish that /forum/ is repeatedly tying up server resources. This makes the forum stack the leading suspect behind the slow-query protection and CPU pressure.