One small-but-important point here: if you’re dealing with a project that’s big enough that “everything does not happen in just one render,” you will need to be sure that you are using the MultiLayer OpenEXR file format throughout, and that all of the necessary “layers” of information are in fact being produced.
Since MultiLayer OpenEXR is a “file per frame” format, render just one frame, then :mad: make(!) :mad: sure(!!) :mad: by actually examining :mad: the actual content :mad: of that one file, before you go to sleep. (Uh huh, voice of painful experience here!)