Hello jhfletcher_1,
Please take the following steps for troubleshooting:
1. Go to Control Panel\System and Security\System, click Remote setting and check if the Windows 8 has enabled the remote control.
2. Check if the same subnet Windows computer can normally RDP to the Windows 8.1.
If they can, the issue is related to the MAC, please ask in the apple forum.
https://discussions.apple.com/welcome
Please note: Since the website is not hosted by Microsoft, the link may change without notice. Microsoft does not guarantee the accuracy of this information.
Best regards,
Fangzhou CHEN