PC is invisible to SMB client apps on same LAN subnet (Xfinity XB6 gateway)

I recently switched from DSL internet to Xfinity cable internet. Before the switch, my cellphones could use a SMB client app to access a shared folder on my Windows 10 PC, to transfer or stream files via wifi. After the switch, the client app displays "unknown host" error and can't access the shared folder. I've read other users' complaints that they can't access SMB remotely from the WAN side because Xfinity blocks SMB port 445, but I haven't found anyone who says they can't access SMB within their own LAN.

Configuration details: Xfinity XB6 gateway. PC is connected to gateway via ethernet. Cellphones connect to gateway via wifi. All devices are listed in gateway Admin Tool interface. Network is set to "private" in Windows so file-sharing should be enabled. SMB app tries to find the PC by the PC's hostname (which the gateway correctly displays) using port 445.