You mean without Cloudflare, right?
2 seconds is not enough to trigger Error 524 in Cloudflare. By default the timeout duration is 100 seconds.
How about before you use Cloudflare? Was your website works fine in HTTPS without using Cloudflare?
Because I’m suspecting that your website was not working in HTTPS previously, so when Cloudflare tries to connect to your server via port 443, your server will not respond.