we have recovered a backup file of a cloud installation (of Discourse) on an own premise server.
The site runs currently without https, this is the only difference between the two instances.
After recovering the backup the old images are not loaded. The new images - uploaded on the new server - do not have any issue …
If you mean hosted by Discourse.org, did you cancel your subscription first or otherwise arrange for uploads to be included in the backup? If not, the uploads are all on their S3 bucket, which might be your problem.
There are several things that won’t work without https. You will need to fix that before doing any meaningful tests.