Thank you - that indeed worked but only comes to show I failed to provide an adequate example as the problem persisted in my application :)

I made an effort to further/better isolate the problem and I think I have a solution. I was starting Dancer2 with a system($plackup $args) command. After looking at the source code of plackup, I started it directly in a fork:

use Plack::Runner;
if (my $ps = fork) {
    $log->info("successfully spawned PID $ps");
    $SIG{CHLD} = "IGNORE";
} else {
    $log->info("starting Dancer2 as PID $$");
    my @args = split(' ', $cmd);
    my $runner = Plack::Runner->new;
    $runner->parse_options(@args) or $log->logdie("Plack::Runner faile
+d to parse startup options");
    $runner->run or $log->logdie("failed to start Dancer2 app");
}
[download]

I need to check whether failures to start are captured correctly, but on the logging front its a win, plus it should be a better way to start it anyway

I still don't know why it was failing before - I did check that processes are running the same version of perl and @INC is the same when started via system() and directly