Lost quest item (Torn Map Piece) after SSF to Trade league migration cannot complete The Runeseeker

I collected one Torn Map Piece for The Runeseeker / Forgotten Bounty quest in Act 4 while playing in SSF Runes of Aldur. I then migrated my character and stash from SSF to the regular Runes of Aldur trade league.
After migration, the quest tracker shows 4 pieces found, but I only have 3 Torn Map Pieces in my inventory and stash. The fourth piece is missing.
I returned to the island where I originally collected it, but the interactable object shows as already collected, so I cannot obtain the piece again. I cannot deliver the pieces to Makoru and therefore cannot complete The Runeseeker quest or unlock the Ancient Runes recipes.
It appears the quest item was lost during the SSF-to-trade migration while the quest progress state carried over.