Option 1 – Modifying termsrv.dll
To have concurrent user sessions working in Windows 10, you need to make small changes to termsrv.dll file. This file is located in C:\Windows\System32 folder. Before modifying termsrv.dll for the first time, you need to take ownership and assign yourself full permissions. You also need to stop Remote Desktop service (TermService) if it’s running.
DLL files can be modified using any HEX Editor (for example Tiny Hexer). You can do this yourself by replacing strings shown below, or just download patched versions from this page.
Windows 10 x64 v1709 – Fall Creators Update (October 2017)
Windows 10 Fall Creators Update (1709 – Redstone 3) updates termsrv.dll to version 10.0.16299.15. To get back concurrent remote desktop connections, make following changes:
39 81 3C 06 00 00 0F 84 B1 7D 02 00
B8 00 01 00 00 89 81 38 06 00 00 90