Sounds like uninformed agents. AS policy states they’ll check through for a layover of less than 18 hours.

https://www.alaskaair.com/content/tr...e/checked-bags

“Travel that includes multiple flights

If your trip includes more than one flight on Alaska Airlines and/or one of our airline partners, we will check your bags to the final destination on your ticket as long as there are fewer than 18 hours between flights.

If you will be in the connecting city for 18 hours or longer, you will need to claim and re-check your baggage. Additional baggage fees may apply.”

I have done this multiple times with overnight layovers. For what it’s worth, I believe a kiosk will by default print the tags all the way through to final destination. I also have definitely encountered agents who claimed max check-through layover is anything from 4 hours to 12 hours.