Computer Strength

I have a very similar problem. I can easily beat level 5 and 6 on the computer but it's a struggle to win against actual people. To answer your question, I thi k that Chess.com's computer is a little whack but it could be that you are just stressing yourself out. If you want to find an average time limit for when you play live chess, try timing yourself when you play against the computer a couple of times. Once you find an average time, you'll feel more confident that you will finish the game before the clock runs out