Any ideas would be welcome.

Hmm, Perl_gv_fetchmeth_pvn finds Bug #121362 for perl5: Bleadperl recently introduced a new SEGV which talks of running bisect.pl - use git bisect to pinpoint changes which you say you kinda did

It also says solution to that deal was Bug #121373 for perl5: Bleadperl v5.19.8-514-ge0e1be5 indicated by valgrind

So, I'd say seek wisdom from the p5p, they might have some tips beyond try that patch ...

Yeah, this is like real c-programming stuff :) way out of my league