Blogger contact widget not working (blocked by CORS policy: No 'Access-Control-Allow-Origin')

Not sure this is a Cloudflare issue. Before adding my Blogspot domain to Cloudflare, the contact form worked just fine. Now it doesn’t anymore. Unfortunately I don’t know exactly when it stopped working, so I can’t point my finger at Cloudflare.
Anyhow, this is what I see in the console every time I try to send a message from my Blogspot site, using the contact form widget:


I’ve tried Development Mode and also disabled proxy in the DNS settings, but still in vain.
Can I get a confirmation that this is not Cloudflare’s fault?
Thank you.

I’m gonna answer to my own question, as I have found the problem.
Apparently Blogger sites do not work very well with Cloudflare. That’s it.

I have exactly the same issue with using custom domain from Cloudflare. Is there any other solution other than leave Cloudflare?