I suspect the IP value of your DNS A record is incorrect. Other ideas follow. Your issue suggests that there may be an incorrect routing or DNS propagation delay. Ensure that your DNS records in Cloudflare match those on your host server. You can also try the following steps:
Log in to your Cloudflare account dashboard.
Click on the appropriate site.
Navigate to the ‘Overview’ tab.
In the lower right corner, find the “Pause Cloudflare on Site” option and click it.
Wait for about 5 minutes for it to take effect, then check if your site is working as expected with HTTPS.
If the site works, unpause Cloudflare and double-check that your SSL/TLS setting is on ‘Full (Strict)’.