I have two these issues that have been coming up for ages. I have disabled all plugins on my site and it still comes up.
A PHP session was created by a session_start() function call. This interferes with REST API and loopback requests. The session should be closed by session_write_close() before making any HTTP requests. The REST API encountered an error
Performance The REST API is one way WordPress, and other applications, communicate with the server. One example is the block editor screen, which relies on this to display, and save, your posts and pages.
The REST API request failed due to an error.
Error: cURL error 28: Operation timed out after 10000 milliseconds with 0 bytes received (http_request_failed)
2. This site seems to crash alot because some of my clients order sometimes in their carts over 250 x different products at a time, but it seems to crash all the time and my client is getting very frustrated.