The errors don't make any sense to me, given that it works in the non-block if and only fails with block-form if. Does this work any better? Does it fail before the if?

sub findString($) {
    my $line = shift;
    my $compiled_regex = eval "qr/$regex/";

    if ($line =~ /$compiled_regex/) {
        print "found\n";
    }
}
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