In this topic the PGIE is running well (as you mentioned PGIE with the model trained by TAO has correct output), the issue here is the classifier has no output.
In the topic-2 it says the detector engine cannot be created as “backend can not support dims:224x224x3”, it seems the PGIE with your model cannot start correctly.
So topic-2 is solved and thus you hit issue (empty classifier_meta_list) in this topic? Thanks to confirm.