Why do my hours get cut every other week yet my coworkers hours always remain the same?

I was hired before two of my coworkers even though one of my coworkers and I started working on the same day but she is a part time employee. My other coworker started a week after I did and she is a full time employee like me if that even matters
Why do my hours get cut every other week yet my coworkers hours always remain the same?
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