I wish my issue was as simple as yours.
I downloaded the app and had the same issue as you. It would only show the current rider list. I was connected via LAN to my PC and the wireless network provided by that modem/router on my android. I tried installing a USB Wireless card into my PC and it still would not work. I uninstalled my antivirus, changed all network settings to open, sharing etc. All firewalls turned off. Any possible setting I changed. STILL it would not show anything but current riders.
I connected to an open wireless network provided by my neighbor, on both my cell phone and my p.c. BOOM it worked like it was supposed to. I do not know why my Modem/Router will not allow the two devices to talk but it wont. I even tried a different router attached to the modem instead of the internal one… that didn’t work either. Super frustrating but no the end of the world.
Just thought I would share my experience.