I have the same issue across a network of websites so it is not an isolated incident. For a multi-billion dollar company Cloudflare has many issues with very little in the way of support.
If you are hosted at siteground the issue is probably as below:
There’s a problem that occurs when Cloudflare’s Automatic Platform Optimization is used along with with siteground Captcha protection mechanism.
When requests from an IP are detected as suspicious by the [Anti-Bot AI a Captcha challenge is visualised. The standard workflow is to solve the challenge and open the requested URL. The Cloudflare system ignores the cache-control: no-cache HTTP header and caches the Captcha page. Then the cached Captcha page is returned to the visitor with the corresponding IP and there is no option to solve it and proceed to the actual website’s page.
The Cloudflare developers are informed for the issue. It should be resolved on their end by implementing an exclude list where the corresponding path (/.well-known/) for the Captcha page can be added. Additionally, the Cloudflare system should honor the cache-control: no-store, max-age=0 headers that we already send for the Captcha page.
The workaround which we can offer from our end for users that want to use the Cloudflare APO is to temporarily deactivate the Captcha protection mechanism.