Sindri can't smith on Sword of Odin, Conquest
This happens on Conquest, any difficulty, with Hippogriff Clan. The central tile is owned and villagers can be put to smith on it, but Sindri gets the red X and is unable to smith on it.
This might be intentional, though I'm pretty sure Horse Warchief can smith on the tile just fine by comparison.
(The tile is definitely owned by myself, it's not neutral or ally-owned, so this isn't related to Sindri being able to mine outside territory.)
Steam Screenshots remove the cursor, so I can't post a screenshot with the red X when Sindri is selected and the tile doesn't have anyone else on it and the Anvil is 0/1 workers.