Select ‘Revise post’ for a pending queued post (that isn’t claimed), don’t select ‘Send PM’ but cancel instead. The text now says ‘You’ve claimed this item and can review it.’ and no x button is next to the text so can’t be unclaimed.
Also, shouldn’t the post return to being unclaimed if prior to selecting ‘Revise post’ the post wasn’t claimed and you’ve opted to cancel when on ‘Revise post’?
Thanks for the bug report, @T_Disco! I’ve just merged a fix for it:
For any reviewable items that are stuck as claimed after you upgrade, you’ll be able to unclaim them by opening the Revise Post dialog, then cancelling out of it.