https://metacpan.org/pod/release/RJBS/perl-5.18.2/pod/perldelta.pod

I don't understand why all the selected bug fixes don't have links :)( bug ids or commit )

some are super cryptic like

A regression from 5.16 in the handling of padranges led to assertion failures if a keyword plugin declined to handle the second ‘my’, but only after creating a padop. This affected, at least, Devel::CallParser under threaded builds. This has been fixed