The current version of Paper is 4.2 Please confirm that you have the most recent version installed. To find out what version you have tap on the Settings icon (sliders) top right and the information will listed at the bottom of the next screen.
Sometimes, performing what we call a “hard reboot” helps when Paper is behaving erratically: First, charge your iPad or iPhone to 100%. Then, hold the Home and Power buttons until your iPad reboots. When you see the Apple logo, release the buttons.
If this doesn't resolve the issue you're experiencing tap on the Settings icon top right, then "Tips & Support", and "Send Logs". This will open an email window with your log files attached. Please describe the issue you're experiencing and then tap "Send". We'll work with you to open a ticket with Paper Engineering.