I just got an Unknown_517 error when trying to unpack an AZW3:
Spoiler:
calibre, version 2.16.0
ERROR: KindleUnpack - The Plugin v0.77.0: 'Unknown_517'
Traceback (most recent call last):
File "calibre_plugins.kindleunpack_plugin.extractio n", line 186, in unpack_ebook
File "calibre_plugins.kindleunpack_plugin.utilities ", line 282, in unpackMOBI
File "calibre_plugins.kindleunpack_plugin.core.kindleun pack", line 870, in unpackBook
File "calibre_plugins.kindleunpack_plugin.core.kindleun pack", line 789, in process_all_mobi_headers
File "calibre_plugins.kindleunpack_plugin.core.kindleun pack", line 542, in processMobi8
File "calibre_plugins.kindleunpack_plugin.core.mobi_opf ", line 103, in __init__
File "calibre_plugins.kindleunpack_plugin.core.mobi_opf ", line 618, in processRefinesMetadata
KeyError: 'Unknown_517'
Kindleunpack has been working like a charm up to this point. It's a magazine file that calibre's ebook viewer can display successfully.