Hi samtrifectatechnology,
Welcome to Microsoft Community.
May I know is the monitor connected by a client or not, when the wallpaper "is replaced by the inbuilt landscape wallpapers"? And are all the adapters have the same sympton? Since you mentioned you are in a company, if the computer are domain-joined, please try connecting the adapter with a computer which is not domain-joined, since sometimes GPO will causes unexpectedly issues.
BTW, would you mind telling how you custom wallpapers so that we can better understanding this issue? Thanks in advance!
Best Regards,
Manson - MSFT | Microsoft Community Support Specialist