This looks like quite new functionality, the docs say ‘experimental’ and the first commit of this code to the WP repo was 6 days ago from date of this writing, so wouldn’t be surprised if you’ll have issues with what you’re doing related to it being in development.
The class that manages block patterns is easy to read:
So you could call e.g. the get_all_registered() method like:
WP_Block_Patterns_Registry::get_instance()->get_all_registered()
or e.g. check if your pattern is registered:
WP_Block_Patterns_Registry::get_instance()->is_registered("your_pattern_name")
I’d suggest if you’re having problems you might either want to wait until it’s a more stable feature or contact the people working on it (e.g. you could start by contacting the person who made that commit as it looks like they’re actively working on it)
HTH!