Defender update broke tethering?

[nukecad]

Here's a bit of an odd one.

Since November (lockdown) I've been tethering my laptop to my phones data via USB.

Yesterday morning that was working as normal. HIbernated the laptop and went shopping, etc.
Woke the laptop Yesterday afternoon and it would no longer see the phone as a router via USB.
(The phone can still be seen, and used as a media device through the same connection).

USB port checks OK, phone check OK, USB cable checks OK.

I could only think that something has messed up the driver for tethering, but I hadn't updated or changed anything and the connection is metered so Windows shouldn't have done either.
The only things that should bypass the metered connection setting is Defender, or MS critical updates.
Looking at the update history there was indeed a defender update applied yesterday.

I also notice that when opening Task Manager 'System Interrupts' are at 100% CPU for a number of seconds, often a sign of a driver problem.

So I can only assume that the Defender update has 'broken' the driver for USB tethering.
Probably just a temporary glitch so I'm not going to mess about with the drivers in Device Manager.

It's not a great problem, I'm just using the phone as a mobile wifi hotspot instead.

[nukecad]

I found the problem, the Remote NDIS Network Device had gone totally missing from Device Manager.

After a bit of head scratching on how to get it back I reset the phone (actually I took the battery out to force a full reset), plugged it back into the laptop USB and turned on tethering.

Bingo, a new, phone specific, RNDIS in device manager and USB tethering working again.

[nukecad]

One interesting thing I have noticed.

Because I'm tethering through the phone on a limited data plan I've been keeping a daily record of mobile data usage.

Looking back through that record, whilst I have been using the Phone as a mobile hotspot since the start of February its been clocking up 1.5x to 2x extra data usage compared to USB tethering.

I'm not doing anything different, nobody else can use that wifi except my laptop, so I'm wondering just why that extra use should be.
Maybe it's other passing phones trying to connect to the mobile wifi and so sending data back and forth?
That doesn't sound right but I do live in the towns market place, so even in lockdown there are a lot of passers by.

I may test that by turning on the hotspot, not connecting myself, and seeing what it does to data usage.