I’m new to OP-1, picked it up about three weeks ago so take this with a grain of salt:
Did you rename the tape tracks? They need to be named “track_1.aif”, “track_2.aif”, etc. Otherwise the OP rebuilds them as “empty” tracks. If so, just rename them on your pc prior to upload.
Another thing to try: shift+> will take you to the end of any track with information recorded on it, maybe your recorded material is in the middle of the tape somewhere?