I bought the Hunting Shortbow (from Dammon, I think?) which is a +1 shortbow with advantage vs. monstrosities and one free casting of Hunter's Mark per long rest. But when I used Hunter's Mark, after slaying my marked target I was unable to use Reapply Hunter's Mark; the option just wouldn't appear even though I had the "Hunt Complete" condition which indicates I should be able to.
This makes the Hunter's Mark extremely tricky to use as I can only use it on targets I expect to survive multiple rounds, and limits the amount of value I can get from the casting. It's still a decent shortbow, but this was really disappointing, and seems like a bug, as nothing in the bow's details makes it seem like the Hunter's Mark is only intended to work against a single target.
I've used the proper Hunter's Mark spell on a Ranger in a previous playthrough and that worked fine (I could reapply it after the original marked target was killed) so it seems like it can work, it just doesn't. Does anyone have the Grymskull Helm to check if that's also affected, as that grants Hunter's Mark as well? I'm not going to be at the Grymforge for a while yet, and not sure the host (it's a multiplayer campaign) is likely to go down that path anyway.