I'm getting this error intermittently on my MAMP box w. Statamic 1.8.4. I think I've managed to narrow it down to line 841 in admin/routes.php.
The offending line reads as follows:
$new_file = $content_root . "/" . dirname($path) . "/" . $status_prefix . $new_numeric . "." . $new_slug . "." . $content_type;
On my MAMP box this causes an extra slash to be inserted, confusing the check if it's the same file later on in the script.
If I "fix" this line to instead use Path::assemble, like the date entry sorting code does it seems to work. Like so:
$new_file = Path::assemble($content_root, dirname($path), $status_prefix . $new_numeric . "." . $new_slug . "." . $content_type);
Has anybody else been having problems with numeric entry sorting?