How do you report hours that vary week to week? (update)

I picked up part-time shifts as a welding apprentice and I am confused about how to report them. This is my first time dealing with any of this. Sometimes my paycheck is late by a week. Who can I ask without risking my claim?

Thanks for writing this out. I went through something close to it 8 months ago, and it settled down once I kept a simple log of every call and form.

I estimated and then checked my pay stub. When there was a small difference I wrote to the agency to correct it.