There’s a link in my post, “standard install” automatically links to the topic that explains what it is 
To elaborate on what Don said, the force https was one available in Discourse admin settings, but not anymore as HTTPS has been enabled by default on Discourse for a long time now (like, 2 years maybe?). So, if needed, this now hidden setting must be enabled via the command line for example.
I suppose 
using a reverse proxy makes your Discourse not a standard install and may have caused the issue you faced (can’t know for sure).
Anyway, enjoy Discourse 
