This might be an already listed bug; happened this morning and got a couple screenshots of it occurring.
When firing a slingbow at its maximum range, it will display the hit as critical and some other random text. The hit is not always critical when this occurs, and this only appears to occur if you’re at the maximum range. As of this patch, that random text is “Fully Repaired”. The previous patch it was something relative to elemental damage.
(those were two separate instances)
Nothing special about the weapon: