Shotgun schema - Error resolving filter expression

We’re seeing a new error on one of our projects, specifically when running “create_filesystem_structure”. We haven’t made a change to the schema, and its identical to many other projects, however I’m only seeing the error on one project.

File "[...]/install/core/python/tank/folder/folder_types/", line 90, in translate_filter_tokens "%s in %s.yml: %s" % (filter_list, yml_path, e) TankError: Error resolving filter expression [{'path': 'project', 'values': ['$project'], 'relation': 'is'}] in [...]/config/core/schema/project/01_Shots/customentity01.yml: The folder object cannot be used in folder $expressions

Here’s the content of that yml file (I don’t see anything labelled/called folder):

# the type of dynamic content
type: "shotgun_entity"

# the shotgun field to use for the folder name
name: "code"

# the shotgun entity type to connect to
entity_type: "CustomEntity01"

# shotgun filters to apply when getting the list of items
# this should be a list of dicts, each dict containing 
# three fields: path, relation and values
# (this is std shotgun API syntax)
# any values starting with $ are resolved into path objects
filters: [ { "path": "project", "relation": "is", "values": [ "$project" ] } ]