Keynote slide transfer problem

After updating Keynote today to version 7.3.1 (I have a MacBook Pro running macOS Sierra), I am now no longer able to copy content from a slide in one presentation and transfer it to a blank slide in another presentation, nor am I able to drag a slide from one presentation to another. When I try, I get the "error" sound, and the slides being moved seem to "float" in place. It's very odd. Anyone have a solution to this, or know why this might be happening? Thank you for your help!