Hi, I can reproduce by doing this
1. Start with a fresh webinoly install : wget -qO weby qrok.es/wy && sudo bash weby 3
2. sudo site domainA.com -wp
sudo site domainA.com -ssl=on
3. domainA.com -> cloudflare SSL Full strict
4. site domainB.com -proxy=[https://domainA.com] -dedicated-reverse-proxy
5. site domainB.com -ssl=on -manual=dns
6. domainB.com -> cloudflare SSL Full strict
Result https://domainB.com -> 502 error
7. Add proxy_ssl_server_name on;
No more 502 error