Codecs, bitrate, simulcast and firewalls

I’m running Jitsi on Ubuntu Server.
At the beginning, with only internal users, I sat minimal resolution 720p, ideal and max 1080p, with h264 preferred.
Unfortunately, with guests I had compatibility issues (browsers not supporting h264) and performance issues (slow computers crashing or not fast enough, with h264 browsers become CPU intensive).

About compatibility, I’m not clear why, with browsers not supporting h264, VP8 wasn’t used instead, it seems when h264 is not supported video stream simply doesn’t start.

About performances, I disabled h264 as VP8 should be lighter and lowered minimal resolution to 360p, with 480p ideal and 720p max.
Simulcast is enabled, but seems to have no effect.
I just completed 2 benchmarks using only fast clients in local network, but I can’t understand why only 1 client was sending 720p while all the others were limited to 360p.

About firewalls, if often happens some ports are blocked, any suggestions about how to configure to mitigate this problem?

Server load and network saturation are low.

Anybody can help to understand and troubleshoot?