I have had this same issue. From emails of proposed merges, that I don't get to immediately, or need some edits on a profile and it may be a day or a week before I get to it all.
Several siblings. I edited the bios over a few days for each. Once I thought I had all the information I could find, I went to pending merges on my watchlist to redo the comparison and none with that LNAB.
Sometimes they show up again? The merge proposals could be found on my Nav pages, but not on pending merges on My Watchlist?