Rather than join in with the same complaint (and I continue to experience this same issue with my iPad Pro 10.5 failing to recognize the Smart Keyboard, especially following iOS updates), try the following:
1) go to System settings > General > Keyboards and see if there is a menu item for Hardware Keyboard
2) if there is, it should be listing the Smart Keyboard with option to change the layout;
3) change the layout from Automatic to U.S. or other keyboard layout that you want.
This will improve connectivity but it will NOT fix the problem 100% of the time.
If you do NOT see a menu item for Hardware Keyboard, press the power key to restart you iPad without having the iPad connected to the charger. Once the iPad is back up and running, check the System Settings again for Keyboards to confirm that the iPad is now recognizing that a Hardware Keyboard is attached. Make sure that you select the keyboard layout that you want instead of the default “Automatic”.
You may also need to use a microfiber cloth to clean the connectors on the bottom of the iPad Pro and on the Smart Keyboard.
Our Apple Genius Bar guy told me that this was likely a software glitch, and I would need to await an update to fix it permanently. That was a year ago. We tried a new Smart Keyboard in the store at the time of my reporting the issue, and using a new keyboard did not fix the problem.
However, the method I outline above has worked for iOS 13.4 until another failure occurs. I use my iPad Pro extensively everyday, and now I have this issue about once a day whereas previously I would average 10 times that amount of trouble.
Hope this helps some of you.