I've experienced this issue several times. One of the latest updates fixed one of the old issues. But there are still two problems occuring, causing guests to get stuck and staff to refuse to work.

If staff are assigned zones outside of another gift shop, they still turn up. But then refuse to work there. Even if you pick them up and drop them there. By unassigning the assistants from any zones fixes this. But defeats the purpose of zoning staff members.

If the assistant is assigned to only restock, or only work on tills, and you've allowed two or more staff members. You can end up with two or more assistants that will only work check out or only restock gifts. It would be good if there's a way of either specifying the extra job role required, or some way to automatically only allow assistants into the specific role required. So there's one of each, a check out and a restocker. Not two of the same, unless there is more than one till! The only work around is to make sure all staff are ticked for both job roles, which again, feels pointless having the two options.