[Hummingbird] Page Caching not working on main site

Page Caching is network active in my multisite (on your hosting) and works just fine on subsites, but not on the main site.

The page_cache.log contains several instances of this, but we can’t find that constant defined anywhere

Page not cached because DONOTCACHEPAGE is defined.

We’ve ensured the option to not cache Forminator form is not enabled, and there’s no other cache plugin active, and have flushed object_cache just in case, but no luck. Can you help?