Trees

The TLDR is that most carts are filled with oil, and oil is a wicking substance. It moves around.

If your cart stops working because it's empty, over time whatever tiny remnants of oil are in the container can wick their way back into a place where the coil will vaporize them again. All of a sudden your dead vape will give you a couple hits if you're lucky.

510 carts are great at flooding the wick/coil area with oil and clogging up too. There's a million ways to reflow the oil to get them usable again but sometimes just forgetting about them somewhere gives them time to fix themselves. If you think it might be clogging you can try something like soaking it (in a sandwich bag or similar to prevent damage) in hot water.

Sometimes the position the cart is in will encourage oil to flow in or out of places.

Sometimes auto draw batteries cause chamber flooding if they don't shut down promptly.

Sometimes the cart gets left somewhere warm and the oil goes anywhere but where it needs to be.

These devices are just prone to issues in my experience, but they aren't that hard to troubleshoot.