Hello,
This seems to be an hardware AND software issue related to ios 11.
After a call with Apple, they asked me to upgrade to 11.2.6 and also test this with another ipad pro (we all have multiple ipad pro isn't it).
I finally found a colleague with another ipad pro, and he was using a logitech keyboard instead.
The logitech keyboard worked fine on my ipad pro, and the smart keyboard worked for some times on his, but after sometimes stopped working (as we know too well).
BUT, when he hooked up back the logitech keyboard, this one was not working either! A reboot was mandatory.
We were able to reproduce the issue on both ipad pro.
SO, it seems that the keyboard, when aging, has bad connection and may have intermittent disconnect, that ios 10 was managing well. SINCE ios 11, intermittent disconnect seems to put the software in a buggy state (buffer overflow or something else) that can be solved sometimes through a reset (Apple procedure), but not always.
I will try another call with Apple to have my smart keyboard replaced, but I doubt the swap will last forever if they dont fix the software issue.
My two cents.