I tried the example for "Respond with content coming from a File containing templates". The callback method "processor(..)" is never called.

request->send(SPIFFS, "/index.htm", String(), false, processor); initializes a new intance of AsyncAbstractResponse class (AsyncFileResponse is derived from AsyncAbstractResponse). Field _chunked is set to true by the constructor. Via some other methods AsyncAbstractResponse::_ack(..) is called.

The problem is that _ack(..) does not call method AsyncAbstractResponse::_fillBufferAndProcessTemplates(..) which calls _callback(..) if _chunked is set to true. But it should! It calls _fillBuffer(..) instead. :-(