From what I can tell, it's not a Caddy issue.   I actually had a similar issue with Traefik as well.   And the people over at Caddy don't think it's a reverse proxy problem at all.   

I have Odoo 16 CE setup through docker-compose.  It works great, even with the reverse-proxy enabled.    I have the website module installed, and use it for an E-commerce site.  

If I turn off the reverse-proxy, and connect to odoo with a direct local ip address, I can reach the website editor no problem.   When I turn on reverse proxy, and connect through my domain, the website editor does not load. 

It's apparently an issue with how Odoo handles requests through a reverse proxy.   Can anyone give me a bit of insight into this?