Update content type template doesn't update or takes days

I have a user who has reported that they have tried to upload a new template to an existing custom content type in a document library. They have found that for one of the content types it worked (but took almost a week to refresh) and for another content type (updated at the same sort of time) it doesn't appear to have updated with a new template. 

Has anyone experienced this or got any advice on best practice when it comes to updating the content type templates? Is it expected behaviour or just a bit flakey? 

Cheers,

Baronne