The reason why this was happening is that the Restrict Banner Rotations prevents custom advertisement code (AKA Google AdSense code, as seen in the Banner Space configuration) from being ran.
This is working as intended, that setting needs to be turned off in order for custom ad code to be ran.
I have disabled that setting and the custom ad code you used is now working.
That being said, I was redirected to a malware site the second I turned off my ad blocker to test the advertisement, so you may wish to choose your ad providers more carefully.