I am still left with Wifi speed issues.
I had the exact same issues. After uninstalling the USB drivers and rebooting the system, the Surface Laptop 3 was bricked. The device was only 2 months old and the issues started immediately after the firmware updates in question. It was working 100% fine prior to the firmware updates.
Microsoft swapped out the device for a brand new laptop. I switched on the new machine, ran Windows Updates and the same Unknown USB Device (Port Reset Failed) started to occur, and the only way to reboot the machine was to hold down the power button for 20 seconds.
I managed to resolve the issues by switching off the Allow the computer to turn off this device to save power options in Device Manager. for multiple USB devices, as well as switching off Stop devices when my screen is off to help save battery. If you're having problems with connected devices, clear the checkbox located in Settings > Devices > USB
I've just joined the Windows Insider Program and received the recommended firmware update which apparently fixes things. I was then able to revert all my manual changes and the system is stable when plugging the USB-C hub in and out.
The one issue I'm still experiencing is that my internet speed goes to a snail's pace when a USB hub is plugged into the machine. The USB hub doesn't have an ethernet port, so I'm unsure as to why it is affecting my wifi speed.
I'm running 100Mb fibre, which works perfectly when the USB-C hub is not plugged in. When it is plugged in, I can barely load webpages, let alone download files or stream video. Sometimes, it seems to completely lose DNS and I get "webpage cannot be found" errors, and Windows shows the wifi as being "disconnected" because it can't resolve DNS. The max resolution I can stream via YouTube is around 480p with buffering. When the USB-C hub is disconnected I can stream 4K without buffering.
I've plugged my mobile phone into the USB-C port, to see if the issue persists across multiple devices, but my wifi worked perfectly fine when the phone was attached. I unplugged the phone, plugged the USB hub back in and the wifi immediately started acting up.