Hey @basdebruin - no changes have been made to the API or the way that error formatting occurs.
The API responds with different error formats depending on the type of error occurring. For example, when I try to run a query with invalid fields, it returns more information (like the message and locations):
The error you posted above is more inline with an error monday is throwing (rather than a GraphQL error such as mine). This could mean a few things - such as hitting the complexity limit or having an invalid template ID.
-Daniel