Champion selection in Ranked downs my ethernet connection

In every (and I really mean every) champion selection for a ranked game my Ethernet connection fails completely. This problem is very specific to Ranked games and limited only to LoL!!

All other applications and software do not down my Ethernet connection. I managed to find a way to keep my connection from getting down. If I start playing a youtube video in Firefox and the connections keeps buffering data, then the connection stays alive.

My settup: System: An older computer with gigabit ethernet on Assus motherboard, AMD Athlon AM3 cpu, GTX1050, current Windows 10 Network: TPlink router, AV500 powerline system connected to PC via ethernet, Onboard ASUS gigabit ethernet (ip connected via open DNS)