Just a punt. Maybe a parent process, system shutdown or something else is sending signals that aren't being handled and are causing general havoc.

One thing to try, if you're not already, is to trap and report on incoming signals, just to see what's going on.

foreach (qw/HUP QUIT KILL TERM/) {
    my $msg = "slugged by a $_";
    $SIG{$_} = sub {warn $msg};
}
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