The problem with your Windows 1809 Enterprise LTSC is that you don't receive any Optional or Recommended Windows Update via Windows Update. AMD latest drivers requires that your Windows is fully updated to work correctly. Since LTSC only receive security updates you can't use the latest AMD Drivers thus you are getting that error. You must use previous AMD Drivers from the year as version 1809 was in use.
Microsoft explains about LTSC Enterprise software: LTSC: What is it, and when should it be used? - Microsoft Tech Community - 293181
From AMD Support concerning Error 1603: https://www.amd.com/en/support/kb/faq/gpu-kb1603
Okay, you also mentioned that you installed previous version with the same error. Read the above support page from AMD Support for troubleshooting tips on how to solve the error.
I suggest if you are able to:
Use free program called DDU (Display Driver Uninstaller) in Safe Mode with the internet disconnected. Then delete AMD Folder C:\AMD from the Root directory. After DDU reboots back into the Windows Desktop, with the internet still disconnected, run the AMD installation package. If it installs correctly then delete again C:\AMD folder to save space and prevent future conflicts with newer AMD Drivers and connect the Internet again.
The internet must be disconnected from preventing another different AMD driver from automatically being installed before installing the current AMD Driver.
Deleting AMD folder C:\AMD will prevent a previous driver files from being mixed when you install the current driver thus possibly causing a conflict and errors since the both use the same exact AMD Folder.
If the above doesn't work then you need to try the other solutions or tips offered by AMD Support or open an Online AMD Service Request (AMD SUPPORT) and asked them for recommendations on how to solve your error from here: https://www.amd.com/en/support/contact-email-form
