When scripts contain html comments (I know... see below), cgjs accepts
single-line comments but not multi-line. e.g.:

{cgjs_add}
<!--- my comment -->
{/cgjs_add}
{cgjs_render}

will work, but

{cgjs_add}
<!--
my comment
has more than one line
-->
{/cgjs_add}
{cgjs_render}

Does not.

The easy workaround is obviously to remove these or comment them out in with
Smarty {* comment *} tags or javascript //comments, but as multi-line html
comments are included with popular scripts such as Google Remarketing, it's easy
to miss them.