The ordering systems have the look and feel of having been bought from one vendor, while their inventory system is from another, and never the twain shall meet. Bar codes were invented for inventory control, and it's a highly refined science. Even produce has a code. But you can't enter a bar code number into the ordering system.
Time slots for picking up your order, that fill up and are unavailable. For many of us who are working from home, our time is flexible. Just tell me an estimated lead time and text me when it's ready. I'll hop in my car or bike and pick up my order in a jiffy.
Now, depending on how the covid pans out in the next year or so, food delivery might have to mature a bit. I could even imagine delivery-only stores, which could have much better inventory control.