the only thing you did not mention is if your chain plates are located outside or inside your hull
so here goes from not knowing if your chain plates are next to or attached to interior
bulkheads then you have a problem. how severe can only be determined by close inspection
. the detents in the hull suggest that your stays/lower shrouds have compressed the hull at the atttachment point. this is either because your bulkheads are soft(rotten), were not bonded properly or the bonding has failed, or the stays/shrouds were over tightened at some point and may still be. or if your hull is cored the hull is cored with foam and the foam may have compressed, or if cored with balsa the balsa has rotted. if there is no support on the inside where this is occurring then that part of the hull has dimpled over time because stress.
there was a boat down here an old Tartan 34 that had the same problem and the buyer had to repair the bulkheads inside. after that he faired the out side with bondo and painted the hull came out well appearance wise, but he had a surveyor
take a look and followed his instructions.
hope this helps