Can't change avatar image via https REST call

When I try to change the avatar on Rocketchat using a REST call:

https://myrocket.it/api/v1/users.setAvatar
Content-Type application/json

with proper parameters and token and the https url of where the image resides, I see a 200 OK code in the logs:

API ➔ debug POST: /api/v1/users.setAvatar
API ➔ debug Success { statusCode: 200, body: { success: true } }

But the avatar won't change.

Steps to reproduce:

1. Make a REST call to change the avatar with the URL of the image which resides on another server (still https)

Expected behavior:

The avatar is correctly changed

Actual behavior:

In the rocketchat's docker logs I see the REST was succesfull:

API ➔ debug POST: /api/v1/users.setAvatar
API ➔ debug Success { statusCode: 200, body: { success: true } }

But the avatar still doesn't change.

Server Setup Information:

• Version of Rocket.Chat Server: 3.6.1
• Operating System: CentOS Linux release 7.8.2003
• Deployment Method: official RocketChat docker image
• Number of Running Instances: 1

Client Setup Information

• Desktop App or Browser Version: Desktop 2.17.7
• Operating System:

Additional context

Rocketchat is deployed with docker on a VM and listens on http, port 3000.
The SSL endpoint is on an Apache Reverse Proxy (hosted on another VM) with proper virtualhost configuration and certificate. The DNS domain is registered and correctly functioning.
If I make a request call directly from the VM or inside the rocketchat container to the URL of the image is retrieved succesfully

I've managed to replicate this architecture on a test machine, which consist of a VM with both Apache Reverse Proxy and Rocketchat (same version 3.6.1), deployed with docker .
In this test scenario, everything works fine and the avatar changes. The only differences are that in this case it's HTTP only and there's no DNS (all custom resolutions are made in the hosts file of both host and container.

Start at the users.setAvatar REST endpoint and reproduce the request against the reported Rocket.Chat 3.6.1 Docker setup. Compare the HTTPS reverse-proxy deployment with the working HTTP-only test, including image retrieval from the server or container. Done means the cause of the successful response with no avatar change is identified and the HTTPS case behaves as expected.