The question being why it blew - cavitation, over-energetic flip, something else?
Commenst as to whether they need to replace the shielding - but that's a lot of weight. Better question is why it blew.
Video clip
https://x.com/mcrs987/status/2057998419335995628?s=20
I think we got to see the consequences of the lack of full blast shielding.
Boostback probably would have gone fine minus one engine had this single engine, either E5 or E6, not had an energetic event and took out 16 of its neighboring engines.
Watch the booster after the flip, you can see the engine blow. Comment elsewhere is why the tried to relight all 33 engines for the boost back?