When the function arguments are written across multiple lines, comments with apostrophes on those lines, break highlighting and consider everything after the single quote as a comment, until the next single quote.
On the highlight.js's demo website (version 11.11.1):
Example (with GitHub's correct highlightning):
<?php
func(
1, // comment's apostrophe
2
);
function func(
$a, // comment's apostrophe
$b,
) {};