I looked around and didn't see this anywhere yet. When you first use your crossbow, enchanted or not, the icon shows a loaded crossbow when there isn't an arrow inside it. So if you forget to load it and return to it, you don't have an arrow ready. It's not a horrific bug, but it is dysfunctional.
Thank you for your report!
We're already tracking this issue at MCPE-53545, so we will resolve and link this ticket as a duplicate.
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