Originally I had an Intel AC 3165 wireless card in my notebook, but I couldn't use simple wireless internet connection and miracast together, one of them was always unusable, so I bought an AC 8265 card. I've successfully installed it into my notebook, I installed the newest drivers, etc... Now everything is a little bit better, I have no lagging issues on screen mirroring, but when I turn on miracast (so when I connect to my TV), the internet speed immediately drops down, my download speed from 3.6MB/s drops down to 20-40KB/s. A simple website is loading for minutes, youtube starts loading videos with 144p (and can't play them either)... This is horrible. I was searching about the problem, and I've found some solutions that helped others: I disabled the "Receive Segment Coalescing State", but didn't helped. I was continue searching, I had run the following commands too:
netsh int tcp set heuristics disabled
netsh int tcp set global autotuninglevel=disabled
netsh int tcp set global rss=enabled
Checked, all values has been changed successfully. I've restarted my computer.
Nothing changed, the problem is still present.
Okay, I continued searching... In an other topic, the problem was the wifi encryption, but I checked, I'm having WPA2-PSK with AES encryption too... The router firmware is also the newest. (TP-Link TL-WR841ND V7, channel 13 (not the same channel as miracast), mode is 11n only for always the fastest speed)
By the way, I'm connecting to a Microsoft Wireless Display Adapter (v2) and I have Windows 10 Creators Update. I started using miracast on this version, so I don't know, if there is any differences with other versions.
I created two reports using SSU, one with Miracast OFF and one with Miracast ON.
I hope, we can find any solutions (that not needs reinstalling the OS).