Ubuntu server UFW strange behavior

[kalpana]

Hi,
I'm anything but a linux expert, so I know that what may sound strange to me could make perfectly sense to you.
Anyway.
My Ubuntu server 20.04 LTS runs a few docker containers like Plex Media server which is in a docker host network.
I can access my docker plex server from my smartphone if I connect to my home router's wifi (a mikrotik device),
BUT if my smartphone is connected to another switch/AP (placed in a different room of my home) plugged to a different port on my mikrotik I can't access Plex anymore.
Even my smart tv connected to the same switch can't access the plex server.
I found out that if I disable UFW everything go back to work flawlessly, but I can't make sense of it since my ubuntu server, my tv, my smartphone and my switch/AP are in the same subnet.
There is still something I'm missing apparently.
Could you help figure this out please?

Thanks