The is a book written by Gordon W Stead, who was the commander of ML126 during WWII, but left shortly before its loss: "A Leaf Upon the Sea: A Small Ship in the Mediterranean, 1941-1943"
Page 160 is written the following:
"While on one last assignment for the Royal Navy I received a signal five weeks later. With hald her crew ashore on leave, 126 had been called from Capri on an errand into Naples and ran into an expired circling torpedo which blew her bows off back to the wheelhouse. She got in under her own power by going astern, to end her days dejectedly alongside the wall in Naples. There was no one in the mess deck at the time of the explosion, and true to her trust, there were no casualties."
Another website (
http://cfv.org.uk/forum/viewtopic.php?f=8&t=43) says that "ML 126 is sunk/CTL after torpedo damage by unknown U Boat off Salerno". This is not coherent with a move between Capri and Naples.
I guess that ML126 was hit somewhere in Naples Bay, and probably closer of Naples than of Capri. The circling torpedo might have been a Flugzeugtorpedo LT 350, that was designed to be launched from high altitude and then do circles in the water. The combination of heavy German losses and no damaged reported in the harbor by the Allied report may indicate that the raid meet heavy defences and so was a total failure, and a LT350 that should had been dropped into the harbour ended in the bay and hit ML126.