Hi! Sketch has been updated already some times. Which kind of tablet are you using? I have an iPad 4th generation and on that one some apps are quite unstable.
As Flora mentioned, Sketch was last updated on December 8. If you don't have that version, try updating because there were some bug fixes.
Can you tell me when it's crashing? And what happens when it crashes? And, definitely let us know what tablet you're using.
Were you able to find success with the previous suggestions? Let me know and we can go from there!