Hi!
We were seeing this, too, and traced it to calls to getting the display name of friends without passing the platform in.
There is one call in UserManagerEOS.cpp that has
else if (Friend->GetDisplayName().IsEmpty())
If you change it to:
else if (Friend->GetDisplayName(Text("Epic")).IsEmpty())
the message goes away.
We had another instance in our own code as well we had to fix.
Hope that helps,
Brent