Surface Pro 4 type cover suddenly not working.

same then I unplugged keyboard and stopped working again.

Like you, I won't consider a Microsoft product from here on in. The Surface Pro is an elegant design, but my verdict now is that it's just not reliable.

Hardware failure would be more understandable. This is not a hardware issue. My Type Cover works on other Surface Pros. Other Type Covers do not work on mine. I have tried every fix suggested by Microsoft, and everything suggested by helpful users here. Multiple times. Nothing. Now I'm left with a $1,400 tablet. I'd sell it except that I'd have to tell potential buyers that the accessory keyboard will not work. Which sort of negates the whole idea of the Surface.

I'll still follow this thread in the hope that someone, somewhere will come up with the definitive fix. I'm not holding my breath.

Today, following an update windows defender antivirus the keyboard has resumed working regularly.

Like you, I won't consider a Microsoft product from here on in. The Surface Pro is an elegant design, but my verdict now is that it's just not reliable.

Hardware failure would be more understandable. This is not a hardware issue. My Type Cover works on other Surface Pros. Other Type Covers do not work on mine. I have tried every fix suggested by Microsoft, and everything suggested by helpful users here. Multiple times. Nothing. Now I'm left with a $1,400 tablet. I'd sell it except that I'd have to tell potential buyers that the accessory keyboard will not work. Which sort of negates the whole idea of the Surface.

I'll still follow this thread in the hope that someone, somewhere will come up with the definitive fix. I'm not holding my breath.

It's ridiculous that Microsoft has yet to acknowledge that this is a problem.  When I brought mine into a Microsoft Store (mainly to confirm that it wasn't the keyboard itself by trying it on another SP4) four months ago, only one of the techs there had heard of the issue after having seen it once before.  Even then, he incorrectly figured it was a hardware failure with the connector.  Either way, there was nothing they could do about it.  It doesn't make sense for anyone to fork over $400 to 1) receive a refurb replacement which 2) could just as easily have the same thing happen to it.  I love my SP4 otherwise, but won't be buying any newer model (have read this affect SP5 and SP6 owners as well) until this is addressed.  I'm still checking this thread here and there for any possible fixes since I haven't seen a new firmware update in a while.  In the interim, I bought a Logitech K830 bluetooth keyboard with integrated touchpad three months ago.

I'm at the stage where I can't even get any sign of power from the keyboard.  Plugging and unplugging the keyboard multiple times does nothing.  Removal of the "Surface Type Cover Filter Device" from Device Manager no longer does anything after reinstallation.  I'd be thrilled if there was at least some kind of beta firmware to test the waters with.   I'm still willing to try options people have found on here that don't seem to work for everyone, but, at the same time, I'm not going to jump through multiple hoops spending a long time working on it.

This fix does not work, it just increases your headache