Using jitsi from two devices from same network (might be mis-use by me or bug)

While I tried to make chat (testing) between two devices on same local network - no picture, voice or text messages were sent between those devices. adding 3rd user from remote network - problem was solved.
To reproduce - you need two devices (computers) at same home, connected via same router to the internet.
first computer using web browser to create new chat, second device gets link and tries to join the chat. I can see that second device on chat, but no video, sound or text is received from each other. adding 2rd device that is out of the local network (connected using another router) solves the problem (all 3 computers can see each other’s video, sound and texts).
tested on two linux computer (firefox 74 and chromium), with one linux computer (firefox) and android phone (internal browser and the application), and (on another network) two windows computer (firefox and chrome, then firefox and edge and latest both with chrome).
in all cases - adding 3rd device (I’ve used computer with linux and firefox) had enabled the chat for all devices.