GE Model gsd2100v55ww

If I remove the hose from the back, the backed up water drains out. There's no clog in the hose or where it attaches to the bottom of the sink (no garbage disposal). There's not an air gap installed but there is a drain loop in the hose. I turned it on its side the other day (for another unrelated issue) and heard something inside. It sounded like something fell but I thought it was the racks. I don't know if this model has a check valve or a ball in it. There's isn't much info online.

The dishwasher is just over a year old.

Any help?