Speaking of which, are there any fan theories on why the boosters seem to have persistent issues? Or is the plumbing still churning fast enough that we keep seeing N=1 issues for successive designs?

The 12th flight was the first to use the third generation Raptors, so this is only their second flight test.

Until the past couple launches it was the ship that had the issues. Had to be blown up a couple times, failed to relight in vacuum, lost an engine and nearly failed to get to the suborbital trajectory last time. Meanwhile the booster had the most spectacular success in the catch, and has yet to result in a catastrophic failure.

The leading theory, from what I can tell, is slosh. The flip on separation is relatively violent, and while there's not much fuel left compared to the amount at launch, it's still heavy enough to do damage.