If you enable filecheck and attachment, then IkiWiki (e.g. via wrapper) will throw a lot of the following errors on stderr

Use of uninitialized value $size in division (/) at /.../filecheck.pm line 73.

73 is

sub humansize ($) {
    my $size=shift;

    foreach my $unit (reverse sort { $units{$a} <=> $units{$b} || $b cmp $a } keys %units) {
        if ($size / $units{$unit} > 0.25) {
            return (int($size / $units{$unit} * 10)/10).$unit;
        }
    }
    return $size; # near zero, or negative
}

Disabling attachment is sufficient to stop this. — Jon 2023-09-06