How to Replicate:

Terminate crossbow loading just as the crossbow sprite in the hotbar shows the string stretched to its fullest.

Behavior:

One arrow/firework is consumed. The crossbow appears loaded but does not play the final "chunk" sound of an arrow dropping into place, and does not shoot the arrow/firework entity when you right-click.

Even if your last arrow/firework was consumed by this bug, the crossbow can still be drawn and the bug repeated; if you draw the crossbow fully, the arrow/firework entity can be fired successfully.

Image is after the bug has occurred and consumed the last arrow. It shows a crossbow being drawn despite there being no arrow.