I doubt the Titanium is eroding although I guess anything is possible.
What your probably seeing is the finish on the face of the cylinder being burnished and or some powder build up from the expanding gases at the cylinder face forcing cone gap.
The 158gr. load shouldn’t be that destructive to the gun, usually it’s the 19 or 20-grain charges of H110 under 125gr. bullets that generate the massive flame cutting conditions associated with this condition and only after many thousand of rounds.
A picture would be helpful here
