Make SSL work for Discourse on Ubuntu 16.04 with Plesk

Hello, I have set up a Discourse Forum System on one of my Cloud Servers with Ubuntu 16.04 + Plesk and multiple Domains on it. The Discourse itself is on a subdomain. I have a very small problem now, at least I think it is small, but for myself I cannot find a solution. When switching to https the Forum does work, but not complete. There are 2 problems: 1. When typing a post in editor, the preview is not shown up - getting error in browser console telling me mixed content isn´t allowed. So system somehow pulls some files from http but actually it should pull them from https 2. When in Discourse backend switching the Forum to force https, I cannot login the admin anymore and I need to rails.c the config to switch that setting off. Details on Installation: Ubuntu 16.04 Plesk Discourse on Docker Image Niginx from Plesk remote proxy to Docker SSL Cert Let´s Encrypt What do I expect from you: Well, I want you to tell me how to fix that problem. The best way for me would be when we are on chat, Discord or what ever you want to. You tell me what to do, I´ll do it. What will that lead to: In future I will need some help for my server stuff. If you are reliable, fast and understand the english language well, I will have upgrade work for you to do -> for example updrade Discourse installation, server upgrades etc. I also have a webshop running on Shopware, there could be some upgrade work too. Looking forward to hear from you guys. Cheers, Daniel