G'day zn553,

Welcome to the Monastery.

As I can see no other mention of it, I thought I'd point out that your first statement has:

... key_path= $private_key_path, ...
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Here's how Perl sees that statement:

$ perl -MO=Deparse,-p -e 'my $ssh = Net::OpenSSH->new($host, user => $
+user, master_opts => ["-vvv"], key_path= $private_key_path, default_s
+sh_opts=>[-o =>"Port=24"]);'
Can't modify constant item in scalar assignment at -e line 1, near "$p
+rivate_key_path,"
-e had compilation errors.
(my $ssh = 'Net::OpenSSH'->new($host, 'user', $user, 'master_opts', ['
+-vvv'], ('key_path' = $private_key_path), 'default_ssh_opts', [(-'o')
+, 'Port=24']));
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Changing '=' to '=>':

$ perl -MO=Deparse,-p -e 'my $ssh = Net::OpenSSH->new($host, user => $
+user, master_opts => ["-vvv"], key_path=> $private_key_path, default_
+ssh_opts=>[-o =>"Port=24"]);'
(my $ssh = 'Net::OpenSSH'->new($host, 'user', $user, 'master_opts', ['
+-vvv'], 'key_path', $private_key_path, 'default_ssh_opts', ['-o', 'Po
+rt=24']));
-e syntax OK
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This comment is not intended to invalidate other responses. However, as you've shown no surrounding code — which could perhaps capture the error in an eval, or similar, block — nor any error or warning output, this may be an additional problem you'll need to address.

If you're unfamiliar with the code I've used, take a look at B::Deparse; and, in case you need it, perlrun has more information on Command Switches.