10.3.x Notes: Number/symbol and keyboard drop keys become dysfunctional

I've marked this '10.3.x' because it occurred in 10.3.1 and 10.3.2. I thought it might be due to the age of my previous iPad, but this is a brand new iPad Pro and it's still happening.

Basically, I can be happily typing away, and tap the number/symbol key and nothing happen. Same with the keyboard drop key - they seem to be the only 2 keys affected. When this happens, I have to close Notes and reopen, then it's fine for a bit, and then it happens again. Restarting/hard resetting doesn't solve anything. I was hoping that the 10.3.3 update might have fixed it but, sadly, no. No other apps appear to be affected.

Anyone out there know what i'm on about…?!