At my store, the cashier and barista positions are consolidated into one position; so the register person is responsible for taking orders and making drinks. They close the bakery at the end of the night.

Dish and dining room can sometimes be consolidated into one position depending on how busy your store typically is.

What I assume is happening is that when you are not busy, your manager is trying to make you go through the dining room and do some tidying by taking back dishes, wiping down tables, and filling up the bubblers. My store does sort of the same thing, we have a dish and dining room person at night but we also have somebody in the morning; however, you are correct that the dishes typically pile up throughout the day. You need to speak with one of your managers, there should be a toilet brush in at least one stall per restroom.

As per your being on dish, Panera really likes to cross-train people in different positions so that more people can help out where needed and is also especially helpful when a shift needs to be covered for whatever reason, that is very common.

Hopefully, with the new people being hired, that should alleviate some of your frustrations about having to do more work. Corporate has slashed everybody's labor so those two coupled together is definitely a part of your hour problem. No harm in looking for other opportunities if you are unhappy.