Let's take a step back, because I'm making stupid assumptions 😄 What version of SilverStripe?
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