Surface Pro 4 type cover suddenly not working.

Yup, it's been happening to SP3, SP4, Sp5, and SP6, so it's definitely widespread.  The other reason we're sure it's not a driver corruption issue (not that i'm saying it may not be occurring as well) is that the keyboard should still be working in UEFI mode without loading Windows and its drivers in the first place.  The only way many us can navigate UEFI now is the tounchscreen.

The MS Support person said to me the fault is in the OS. It corrupts the keyboard driver. This is why driver replacement works for only a short time and then the issue returns (presumably the driver taking a little while to get corrupted again). If this isn't fixing it, then its hardware, but he did not elaborate on what the hardware fault could be.

In trying the Firmware update, did you also update to the latest OS -at the same time- ?  ...otherwise the old OS is still there to cause corruption.

I wasn't aware this issue was going beyond the SP4, thats quite major if it is.

OK, fair enough I hear you.

Latest SPro4 Firmware release May 2019, tried that?

https://www.microsoft.com/en-us/download/details.aspx?id=49498

...and if it is Firmware and nothing else, why did MS replace my SP4 in the past few weeks and not just get me to download the above?

A Firmware update is/can be incorporated as part of the OS update or even MS updates.

In trying to think of one explanation I can think of, perhaps there was some very small hardware change during the production time of the SP4, and the earlier type is susceptable to this keyboard issue when the software hits it?  As an example, the Xbox360 had a fault called the 'ring of death', a hardware change was then made to prevent this fault, but it was still the Xbox360, the only way to tell was to look at the manufacture date to know.

Thanks, AndrewT111111, but I tried that firmware as soon as it came out.  Had no effect, I'm afraid.  Even after 4-5 attempts. It's definitely not a hardware change.  It happens to most people only right after a firmware update, including to SP5 and SP6 owners who have complained.  Seeing that it's not model-specific is even more disheartening.  For most people, the firmware update goes without a hitch.  Even though mine didn't appear to have any issues, the keyboard stopped functioning afterward.  Deleting and automatic reinstallation of the drivers would briefly cause keyboard detection to work, then it'd fail again.  SP3-SP6 users fight with it, try the keyboard on another Surface Pro, the keyboard works fine.  Try any keyboard back on the afflicted units, no luck.  The last major thing I tried last month was to manually delete the Surface Type Cover Filter Device (which had renamed itself to a generic "HID keyboard device"), but this time it didn't automatically reinstall itself, not showing up when showing hidden devices in Device Manager.  Not that it did much good when I still had it after the initial failure over 4 months ago.  I did see one post recently mention that trying a newer version of the type keyboard (which would force an updated driver) worked, but only briefly.

OK, fair enough I hear you.

Latest SPro4 Firmware release May 2019, tried that?

https://www.microsoft.com/en-us/download/details.aspx?id=49498

...and if it is Firmware and nothing else, why did MS replace my SP4 in the past few weeks and not just get me to download the above?

A Firmware update is/can be incorporated as part of the OS update or even MS updates.

My firmware/UEFI version is 108.2439.769

In trying to think of one explanation I can think of, perhaps there was some very small hardware change during the production time of the SP4, and the earlier type is susceptable to this keyboard issue when the software hits it?  -And this is why some people get this issue and others don't, and some can fix it by software and others cannot.

As an example, the Xbox360 had a fault called the 'ring of death', a hardware change was then made to prevent this fault, but it was still produced as the same Xbox360, the only way to tell was to look at the manufacture date to know.

The problem remains that no clean install of any version of the OS, 1903 or otherwise, is going to resolve a firmware-based issue.  It's not a hardware failure either as opposed to a firmware issue making the hardware detection act completely wonky.  It's also not worth the hassle to me to do a full battery drain to get the keyboard to work again if it's not a permanent solution.  As some have said before, we really need a new firmware or beta firmware that actually addresses the issue since we have no way, unfortunately, of rolling back the existing firmware.  I would say that, yes, a class action lawsuit could be called for here.  This problem affects multiple versions of the Surface Pro, and getting it replaced is no guarantee it won't recur.  It's more a matter of luck of timing as to whether you get it replaced in-warranty or at-cost.

This would be less of a pain if good alternatives existed that didn't cause more inconvenience or lessen portability.  All other keyboard/touchpad combos require separate charging.  Bluetooth versions tend to have more lag.  And wifi-based ones generally require one to use up the Surface Pro USB port on a dongle.  Nevermind that the Surface Pro touchpad is good enough to make many other options feel inferior.  At this rate, I would expect the eventual Surface Pro 7 to either have the same issue, or to have it resolved but without any acknowledgement from Microsoft that anything was done or that prior versions can be fixed.  I hope I'm wrong, but I've also been hoping to see this fixed when it affected me over 4 months ago then let that hope pretty much leave when i saw this thread and other mentions of how long this situation has existed.  In the interim, I'll just make do with the Logitech K830 keyboard w/touchpad that has helped alleviate things for now.  But thanks again to everyone who brings any new info to light on possible solutions.  I'm still trying to at get my "surface type cover filter device" reinstalled since it didn't return after the last deletion.