Undefined variable: class

Hi,

We’re getting the following error on our client’s staging site (file path changed):

Notice: Undefined variable: class in **/wp-content/plugins/accelerated-mobile-pages/includes/vendor/amp/includes/sanitizers/class-amp-img-sanitizer.php on line 94

Plugin version is 0.9.97.36.

This isn’t appearing on every page so is a bit tricky to debug. Would really appreciate the plugin developer’s input on this.

Thanks