Bizarre keyboard behaviour when trying to set up my new S5

[AC Question]

I'm trying to set up my S5, but the keyboard is acting so weird. In order for anything to appear, I need to press and hold a key, and then double-tap the key for the character to appear. Incredibly frustrating. I've googled endlessly with no luck. Please help.

 

[B. Diddy]

Welcome to Android Central! How old is the phone? Did that just start happening, and was it normal before?

Try wiping the system cache partition, which won't erase any personal data: Reset: Samsung Galaxy S 5 | T-Mobile Support