I was in the process of troubleshooting this on my own since Microsoft doesn't seem to want to really look at it, and this is what I found on my Surface Book 2. I have the biggest fastest one they sell and dropping WiFi is unacceptable. I purchased a stand alone WiFi adapter, disabled the Marvel adapter and my connection speed was great with no dropouts. But then I discovered the Bluetooth no longer worked. So the Marvel adapter is WiFi and Bluetooth. I re enabled the Marvel adapter and just turned off Bluetooth. Great speed and no dropouts. The surface pen still works with Bluetooth turned off it just doesn't have the shortcuts on the button. I changed my mouse over to a non Bluetooth mouse and everything is still great.
On my unit it seems the Marvel adapter can not do both active Bluetooth and WiFi at the same time. This is a driver issue for sure, it is mixing the signals and dropping WiFi over Bluetooth. I also notice that Bluetooth was lagging but assumed it was the mouse, It wasn't. The Marvel adapter needs a complete re wright on the drivers.
Microsoft and Marvel need to get this resolved before they completely lose all respectability with their customers.