I see, the permissions should be correct. 775 for all of the forum-xxxx folders, 644 on the files.

What permissions are required?

The pictures I showed are clear enough when they are viewed outside of the forum, for some reason simple-press tries to squish images too much.

Go to 

2017-09-01 - 16.06.06 ~ Cropped Capture

 in your browser and it'll look fine, of course no permissions will show on the files/folders in that picture because that's on my local system. Comparing what files/folders exist between the test site and the live site and what changes there are to the actual code on each file.

Red = difference in code between the two files (the two it flags is just that one includes the subdomain and one doesn't)
Purple = Exists on one, doesn't exist on other.

Disabling the cache doesn't help either (Psst it's in global settings not general settings)