First, make sure that you're selecting all the snippets you want to include in your mash. Take a look at this article if you're not sure how. Also, verify that you have the "Favorites" option disabled in the mashing screen.
If your mashing settings are correct and your video still doesn't include all the snippets, skips some, or you get an empty mash, you must know this is something we're working on fixing.
Please try tapping on the private snippets button (red eye icon at the top) in the "Choose Dates" > "Custom" screen and mashing with this option selected.
If that doesn't work, there's another workaround that you can try. You'll need to sign up for our 7-day free trial of Pro—you can cancel at any time, and you won't get charged if you cancel before the trial ends. If you're already a Pro user, you're good to go!
Once you're on Pro:
Create a full backup, making sure it contains all of your snippets.
Repeat the mashing process.
That's it! Your mashed video should now include all the snippets you selected.