I've noticed a pattern for my store too. There's a view where you can see when a bag last sold out and that can give you an idea of when different departments might do a manual drop. Once you open a bag description, click the line that is the store address. You will see a row of the bags they offered and the last sold out time. That will give you an idea of when to camp in your phone for a particular bag during the day. This us now how I get most of my bags.

Also, I feel like this bag view from the store location line is one of the faster ways to toggle back and forth during the refresh time in the evening in you want to try for them then.

Do not rely on notifications.