I can't solve the problem, but that info turned out to be sufficient for me to guess where to poke. I can reproduce a segfault in just 7 lines of code.
File: mx_segfault.pl
use lib '.';
use Demo;
File: Demo.pm
package Demo;
use MooseX::Extended;
require Stuff;
File: Stuff.pm
package Stuff;
use MooseX::Extended;
With this code,
perl -wc mx_segfault.pl segfaults, and
valgrind throws a 455-line tantrum.
==12066== Memcheck, a memory error detector
==12066== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et
+al.
==12066== Using Valgrind-3.16.1 and LibVEX; rerun with -h for copyrigh
+t info
==12066== Command: perl -wc mx_segfault.pl
==12066==
==12066== Invalid read of size 2
==12066== at 0x251CCD: S_pop_eval_context_maybe_croak (in /home/haj
+/perl5/perlbrew/perls/perl-5.36.0/bin/perl)
==12066== by 0x25FFA0: Perl_pp_leaveeval (in /home/haj/perl5/perlbr
+ew/perls/perl-5.36.0/bin/perl)
==12066== by 0x213312: Perl_runops_standard (in /home/haj/perl5/per
+lbrew/perls/perl-5.36.0/bin/perl)
==12066== by 0x177DFD: Perl_call_sv (in /home/haj/perl5/perlbrew/pe
+rls/perl-5.36.0/bin/perl)
==12066== by 0x17A70D: Perl_call_list (in /home/haj/perl5/perlbrew/
+perls/perl-5.36.0/bin/perl)
==12066== by 0x15E84A: S_process_special_blocks (in /home/haj/perl5
+/perlbrew/perls/perl-5.36.0/bin/perl)
==12066== by 0x170805: Perl_newATTRSUB_x (in /home/haj/perl5/perlbr
+ew/perls/perl-5.36.0/bin/perl)
==12066== by 0x1743DA: Perl_utilize (in /home/haj/perl5/perlbrew/pe
+rls/perl-5.36.0/bin/perl)
==12066== by 0x1B000E: Perl_yyparse (in /home/haj/perl5/perlbrew/pe
+rls/perl-5.36.0/bin/perl)
==12066== by 0x17E836: perl_parse (in /home/haj/perl5/perlbrew/perl
+s/perl-5.36.0/bin/perl)
==12066== by 0x155295: main (in /home/haj/perl5/perlbrew/perls/perl
+-5.36.0/bin/perl)
==12066== Address 0x4c2528a is 314 bytes inside a block of size 1,872
+ free'd
==12066== at 0x483AD7B: realloc (vg_replace_malloc.c:834)
==12066== by 0x1F385C: Perl_safesysrealloc (in /home/haj/perl5/perl
+brew/perls/perl-5.36.0/bin/perl)
==12066== by 0x24D3BB: Perl_cxinc (in /home/haj/perl5/perlbrew/perl
+s/perl-5.36.0/bin/perl)
==12066== by 0x21CED4: Perl_pp_entersub (in /home/haj/perl5/perlbre
+w/perls/perl-5.36.0/bin/perl)
==12066== by 0x213312: Perl_runops_standard (in /home/haj/perl5/per
+lbrew/perls/perl-5.36.0/bin/perl)
==12066== by 0x25130B: S_docatch (in /home/haj/perl5/perlbrew/perls
+/perl-5.36.0/bin/perl)
==12066== by 0x213312: Perl_runops_standard (in /home/haj/perl5/per
+lbrew/perls/perl-5.36.0/bin/perl)
==12066== by 0x177C5A: Perl_call_sv (in /home/haj/perl5/perlbrew/pe
+rls/perl-5.36.0/bin/perl)
==12066== by 0x87D828C: call_after (in /home/haj/perl5/perlbrew/per
+ls/perl-5.36.0/lib/site_perl/5.36.0/x86_64-linux/auto/B/Hooks/AtRunti
+me/AtRuntime.so)
==12066== by 0x24F7A1: Perl_leave_scope (in /home/haj/perl5/perlbre
+w/perls/perl-5.36.0/bin/perl)
==12066== by 0x251CCC: S_pop_eval_context_maybe_croak (in /home/haj
+/perl5/perlbrew/perls/perl-5.36.0/bin/perl)
==12066== by 0x25FFA0: Perl_pp_leaveeval (in /home/haj/perl5/perlbr
+ew/perls/perl-5.36.0/bin/perl)
==12066== Block was alloc'd at
==12066== at 0x483877F: malloc (vg_replace_malloc.c:307)
==12066== by 0x1F3502: Perl_safesysmalloc (in /home/haj/perl5/perlb
+rew/perls/perl-5.36.0/bin/perl)
==12066== by 0x24D316: Perl_new_stackinfo (in /home/haj/perl5/perlb
+rew/perls/perl-5.36.0/bin/perl)
==12066== by 0x15E9D6: S_process_special_blocks (in /home/haj/perl5
+/perlbrew/perls/perl-5.36.0/bin/perl)
==12066== by 0x170805: Perl_newATTRSUB_x (in /home/haj/perl5/perlbr
+ew/perls/perl-5.36.0/bin/perl)
==12066== by 0x1743DA: Perl_utilize (in /home/haj/perl5/perlbrew/pe
+rls/perl-5.36.0/bin/perl)
==12066== by 0x1B000E: Perl_yyparse (in /home/haj/perl5/perlbrew/pe
+rls/perl-5.36.0/bin/perl)
==12066== by 0x17E836: perl_parse (in /home/haj/perl5/perlbrew/perl
+s/perl-5.36.0/bin/perl)
==12066== by 0x155295: main (in /home/haj/perl5/perlbrew/perls/perl
+-5.36.0/bin/perl)