How's your theme configured in your YML?
That I’ll have to get back later, am away from desk
idk if this helps... but ive had that once wehre i needed the first word after the _ to be lowercase
it only occured on deployment servers not localy maybe a mismatch of phpversions?
@phyzical holy moly that worked
Are you developing on (for example) Windows and deploying to a Linux machine?