When the net ops turned on proxy authentication at our work using NTLM our solaris systems had problems. Firefox etc can set up authentication but others use environment variables like
http_proxy
Solution was to put authentication into variable. Bit of a bummer since need to update it every 90 days but in most cases it does work.
Maybe you can do something similar in you proxy setup line
...
$mech->proxy(['http', 'ftp'], 'http://user@password:10.16.5.11:3030');
...