Change your driver to be a Microsoft generic driver rather than one from Marvell.
1) Start Device Manager
2) Select your Marvell AVASTAR Bluetooth Radio Adapter
3) Right-click, then choose Update Driver
4) Choose the second option: Browse my computer for driver software
5) Choose the "Generic Bluetooth Adapter", Next, then Close after it installs.
And again, let us know if this fixes your troubles.
By the way, the issue may be regarding compatibility with your router. The cause is not yours, however, but may be an oversight by Microsoft or Marvell engineers.
This is so crazy. I experienced the exact opposite! Installing the Marvell drivers have been a God Send and my Surface Pro 6 is BLAZING fast now! I would never go back to generic drivers, but hey, as long as they can function when the Marvell drivers do not. I guess it works! lmao