Rules not working as expected - tags don't fire

Rules not working as expected - tags don't fire

I'm setting up tracking on Google Tag Manager today and am having some
trouble with rules.
I have a custom HTML tag where I'd like to fire only on a given page:
https://example.com/index.php/page/index/10
Call the rule "Page 10". In rules I have tried:
url equals: https://example.com/index.php/page/index/10
url contains: page/index/10
url ends: page/index/10
url contains: page/index/10
When this rule is applied to the tag in question it does not fire. I know
the tag works because when I apply another rule to it, all pages (url
regex .*) it works fine. But, this tag must only work on page 10.
Is anything apparent from the info given? I'm not sure what else could be
relevant?