@Kevin_Z Iam Connected to the second router, but i also tried connected to the main router and its happening too.

@Kevin_Z Thanks for reply. As you said, my ping is "good". When Iam testing it on page internerconnection i have stable 8ms ping, which is great. On the website there are now peaks showed, also in...

My internet provider changed wifi routers to TP-LINK model: archer C6. - AC1200 Wireless MU-MIMO gigabit router. I have 2 wifi routers in our flat. One main router (master) and the second which is...