I confirmed that the ItemChannelLink json file had a link to an Item that had been previously been deleted. If I created a new item with the exact same name it would automatically already be linked to the channel and I could unlink it successfully.
That was a pain so I used the API Explorer which had an endpoint to do the purge /links/purge. The purge deleted 23 of these and this issue is solved for me. It appears that this issue was not related to Zwave in the end but rather related to these orphaned links. Thanks all who assisted.
It appears that rlkoshak provides information on how to detect and remove orphaned links in this prior thread: OH3 Broken links on items after upgrade from 2.5.10 - Setup, Configuration and Use / Migration - openHAB Community . I did not confirm this would have worked for me, but it seems likely, would have gotten me there hours earlier, and seems a better way to do it.
Quoting rlkoshak:
From the Karaf console run
openhab:links orphan list
will show all the broken links and
openhab:links orphan purge
will delete them all.