I wasn’t quite sure where to put this on the forums, but I have discovered something that may be intended, but I assume was just unaccounted for. My steam.exe was previously located on my D: drive because it was my main drive before I got an SSD. As such the steam overlay never worked with the Steam Online Subsystem plugin, however the issue was resolved after moving my Steam.exe to my C: drive. I am merely suggesting UE4 search other drives for the Steam.exe as many people I know have had this issue and I came across it after one of my playtesters reported it worked on his machine.