get_avatar ignored in one template file

I have three multisite installations all using the same theme. get_avatar() does not work on one page of one of the three.

Even when I put this in that page – home.php – to test, nothing at all shows up:

<?php echo get_avatar( '1', 64,get_template_directory_uri().'/i/anonymous.png' ); ?>

It works fine in other pages in the same installation, but in home.php get_avatar() is ignored no matter where in the file I put it.

I have cleared caches.

Anything else I could try?

Can get_avatar clash with anything? Does it require something?

Are there known get_avatar bugs that could cause this?