I have a very similar setup and it seems to work fine.
Are you using the orange cloud option in the dns settings?
You used a certificate generated from the 'origin server' option on cloudflares SSL/TLS option right? I used and .pem and .key file. I didn't see a .crt file option there.
certificates:
- certFile: /traefik/mysite.pem
keyFile: /traefik/mysite.key
Do you have a univeral certificate for your domain and wildcards in the 'Edge Certificates' section of the same cloudflare menu? This is the certificate that CF would serve when visiting your site.
Have you tried clearing the site cache and putting your domain into 'development' mode on cloudflare?
These are things that gave me trouble at the beginning 