Braces elastics keep snapping?

I've had braces for just over 2 months, and got elastics put in today.
The orthodontist said to have them in 24/7, even when eating, sleeping, etc.
I've noticed that they either keep snapping, or lose the strong pull in them after a very short amount of time.
Is this normal? What can I do/not do to stop them snapping?

Braces elastics keep snapping?
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