EX2800 Windows File Sharing (MR6400 mobile hotspot)

I'm configured with PCs connected via ethernet to the MR6400 mobile hotspot and portable devices (Windows laptop, android tablet, Chromebook) connected to the EX2800 WiFi extender. Wired devices can share with each other and wireless devices can share with each other, but wireless devices cannot connect to wired PCs.

Any ideas on how to fix this? NAT issue? Firewall?

Network sharing is set up as Private - username/pwd required and all are in the same Workgroup.