Hello @mobilityrising,
Thanks for notifying me!
This notice means that the single term item assumed to be available can’t be located.
It also means that no breadcrumb name will be assigned for the term item… which is something I’ll need to think about for the fix as the breadcrumb entry is now invalid, and possibly other items within that crumb are also incorrect.
Perhaps, by any chance, you do not have a category assigned to the post where this notice occurs?
Generally speaking, WordPress does not allow this behavior. This can only be possible if the previously assigned category has been removed later than the post has last been saved.
Nevertheless, a notice is nothing to worry about, it’s basic PHP standards enforcement. But it means I’ve left out an availability check and I’ll get that patched up in the next update.
I hope this clears things up, have a wonderful Sunday!