Several others have mentioned this, but I’ll add to the list. For me it is entirely tied to WiFi and iOS 11.x. Both my Smart Keyboard and my external (Bluetooth) keyboard are doing this. As long as I am at home, I can use my iPad whenever I want, it will come out of sleep and work just fine. The minute I take it to work (or anywhere else where there is a splash-screen, public wifi) the keyboard stops working. As others have said, the keyboard IS being detected because the on-screen keyboard disappears, but entry from any key is not detected. Restarting the iPad, then rejoining the public (I.e., not my home) WiFi, makes everything work fine. Interestingly, if I leave that public place and return to my home WiFi, I never have this issue; it jumps back onto my home wifi perfectly and the either keyboard works fine. This is clearly tied to iOS 11.x and public WiFi spash-screen access. I have submitted several times now to Apple. Hoping a later revision of 11 fixes this.