No reason other than user error for copy/paste not to work I can think of. If so, you shold be able to find a 'lane' containing your pasted notes. If that fails, create a new MIDI track and paste the notes at the beginning of the new track just to make sure you're copying and pasting - if the notes don't show up in the new track, either retrace your steps until you get it to work or give support a call. If it's still not working as you expect, turn on track layers on the target track - the notes may be hidden behind the existing clip in the track. make sure the target track is selected and the 'now time' is set to the location in the track where you want to paste.
I think the key and the first things to check are that you are copying the notes you think you are and pasting the notes where you think you are. Wow, it took a month to try that? LOL!! (just kidding!) Isn't there something where I can play a rhythm for a few measures and it extrapolates and loops it? It says 'undo paste' but no extra notes show up.