The error message about transport seems to be coming from your server at port 3001.

Can you get a "tcpdump" to capture it ?

Here is the code snippet (in AnyEvent::PocketIO::Client) that is catching the error:

            $socket->on_read( sub {
                return unless length $_[0]->rbuf;
                return if $read;
 
                my ( $status_line ) = $_[0]->rbuf =~ /^(.+)\015\012/;
                my ( $code ) = $status_line =~ m{^HTTP/[.01]+ (\d+) };
                my $error;
 
                if ( $code && $code != 200 ) {
                    $_[0]->rbuf =~ /\015\012\015\012(.*)/sm;
                    $error = { code => $code, message => $1 };
                    $read++;
                    $cb->( $error, $self ); #<<< Line # 86 <<<<
                    return;
                }
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Since the "code" is displayed as "0" it is very strange that it it is passing the "if" check.

I suspect the "$code" contains something like "00", which is later displayed as "0".