If you setup a redirect rule in Cloudflare that is matched on the hostname, it will also apply to both HTTP and HTTPS.
Strictly speaking, a “redirect” only happens when you are sent to a new URL. There is no such thing as a “masked redirect”, URL masking is fundamentally different than redirecting, and technically that’s just an iframe that embeds the new site.
There are a couple of reasons that come to mind:
The specific redirect method you’re using actually uses URL masking.
The redirect doesn’t apply at all, and you’re just viewing the website you had uploaded to your subdomain with us.
There is some kind of weird caching issue that results in viewing the old page on HTTP but not on HTTPS.
In any case, it’s hard to help you when all we have is your description to go on.
Can you please give us the real URLs so we can see for ourselves what’s happening on it?
And could you please clarify which exact method you used to setup the redirect (our Redirects tool, Cloudflare, a setting in your website, custom .htaccess rules/HTML/PHP/Javascript)?
Thanks for your help. It seems the problem was caused by Firefox browser. I eventually set up the redirect in Cloudflare, but it works only in browsers other than Firefox.