I've got several problems with my WiFi and Bluetooth.
First my Bluetooth driver disappeared during usage and disconnected my pen and mouse. With uninstalling the driver and installing the new version i solved this one.
The other issue is the WiFi download speed. It decreases from 600-800 kBps to 100 kBps and sometimes even cancels the download.
I tried a 200MB-download from an university server which took over 40 minutes. That's way to long for a device like this.
At home I tested MS Edge, Opera and Firefox for downloading the same file with the same result for each browser.
My FritzBox is up to date and I also uninstalled the Intel wireless Dual Band ac 8265 and reinstalled it without success.
Next i took my Samsung Galaxy S6, a 5-year old Lenovo Notebook with Win7 and another Lenovo with Win8 to download the file. All devices reached download speeds around 2 MBps.
On top of that I used HP Mobile Connect Pro to download the file on my Elitebook. Surprisingly I reached a download speed around 1.7 MBps.
I don't know where to search for other points which cause this issue.
Can this be a Win10 thing? Sadly I've no other Win10 device around.
Is this a hardware problem with the antenna?