When I was trying to find a fix for my surface book, I came across this which is actually for the surface pro 4:
https://www.youtube.com/watch?v=h6WyBOcf5Ew&list=WL
In the comment section, the guy describes how he fixed it:
* Cause
1. I booted my SP4(SurfacePro4) with low battery condition.
2. It booted, displayed 'Surface' logo and powered off immediately. (no loop)
3. I guessed it was just low battery problem. So I began to charge it.
4. Charging SP4 for a couple of hours, I booted it again.
5. It falled into 'Boot Loop'. It seems to be endless repeating of #2.
6. Nothing to do with SP4. Can't enter UEFI or OS reinstall.
* Solution
1. Discharge SP4 as possible as you can. Let SP4 boot loop alone. (in my case I've saw boot loop for 6 hours. painful)
2. It gets hot. Be careful for the heat radiation.
3. When it's fully discharged, it'll be powered off eventually.
4. Turn on SP4 again, and you can see a 'Big LOW BATTERY Icon' followed by 'Surface' logo. (and then powered off automatically)
5. Seeing ' Big LOW BATTERY Icon' is IMPORTANT. It makes a big chance to exit from the boot loop.
6. Try #4 repeatedly to discharge it as far as you can.
7. If it's entirely discharged, pressing the power button takes no effect.
8. OK. Now charge SP4 at least 15 minutes.
9. Push the power button. Voila~!
I'm trying this out not for my surface book, but not sure it will work as this seems to be more specific to the surface pro 4. But you should give this a go and see if it works for you.
I'll be trying this as well while I'm at work. (Surface Pro 6)
I'm curious if this is similar to removing the CMOS battery on a desktop PC thereby essentially resetting the BIOS/UEFI.