I have multiple mobile devices on my network with 4 Roku devices. Only 2 of the mobile devices will connect to the Rokus as a remote. The other devices get the error that they are on a public network even though they are not and have a 192.168 IP Address. Some of the devices are a ASUS Chrome Tablet CT100, ASUS Chromebook C302 (with Android Apps), and a Lenovo Thinkpad 13 Chromebook (with Android Apps).
Do you have your wireless configured with guest access, as well as private (usually two different SSIDs)? If so, some of your wireless devices might be connected to the guest access, which blocks any connection to your private network devices. Make sure all of the wireless devices are in the same IP address block, i.e. the first three digits are the same. Such as 192.168.1.x. If the third digit differs, and you haven't done something out of the ordinary with your router, then they are on different subnets and again can't see each other.
Dan Roku Stick (3600), Ultra (4640), Ultra (4670), Ultra (4800), Premiere (3920), Insignia 720p Roku TV, Sharp 4K Roku TV, Nvidia Shield, Windows 10 Pro x64 running Serviio and Plex on a wired Gigabit network.