Hi Destineo,
Welcome to the Apple Support Communities. It sounds like you're running into an issue using the Time Lapse feature.
Can you provide some detail about what happens when you say it's stuck on loading?
How long is the time lapse video you've recorded? Does it seem to work as expected if you take a short time lapse video?
When you say the footage can't be used, are you getting an error of any kind?
Are you using iCloud Photos?
The answers to these questions will help work out what might be happening. As a starting point, try to Restart your iPhone, iPad, or iPod touch to see if this helps. Ensuring your software is updated to iOS 12.1.4 is a great idea as well: How to back up your iPhone, iPad, and iPod touch and Update your iPhone, iPad, or iPod touch
I hope this helps get you started.
Take care.