@PeterBosko So it is a behaviour of my internet provider device. Thank you for your advices !

@Ivaylo Yeah, I have suspision that my internet provider is resposible for this behaviour. I contacted him, and 'll see what will he suggest. I will close this as soon as I will have answer and solve...

@Ivaylo DMZ was disabled. So no change. UPnP was enabled, so I disabled it, but redirect still happens. Thank You

@PeterBosko Looked promising - until I found out, that Remote management was already disabled in my settings. What could be another case causing this behaviour? On what device is even runing that...

@Ivaylo It is server in my infrastructure, to which I want all 443 requests to be redirected. However it is not reached, because that redirect happens. Thank you

@Ivaylo I'm not aware of any Ubiquiti device. However I have LG TV connected to router. Here is the router Virtual Servers configuration Thanks