PHP $_SERVER[‘DOCUMENT_ROOT’] removed a slash

I read other posts about $_SERVER[‘DOCUMENT_ROOT’] (like this) but what happened to me is that all the pages in my website basically lost the slash overnight.

I didn’t change anything neither to the pages nor the config files…
What can I have done wrong to trigger this?

Is there a faster way to solve it than just update every single page?
I use $_SERVER[‘DOCUMENT_ROOT’] . ‘/folder/library.php’ pretty much in every file, so it’s going to take a while (and a lot of pages not working) before to correct them all.

TA