Your code does not compile. You are missing closing /'s at your substitutions. You probably originaly meant

#!/usr/bin/perl
use strict;
use warnings;

my $s = << '__STRING__';
hubba1
bubba
hubba2
__STRING__

$s =~ /bubba/gm;
$s =~ /no match/gm;
print $s =~ /(hubba\d)/gm;
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This is the documented behaviour. Add the /c flag to the second match to keep the position even after the failed match. See perlre for details.