Currently I'm in the same position too after attempting the update for the mech beast on the DMM player also so maybe something went wrong when I was editing the file for the 0_download? Messing with copies right now but no results yet.
For the DMM player, did you manage to to get the Ayakashi Rumble characters' scenes? I haven't needed to modify anything besides 0_download_json, so if the subsequent steps are what's falling I don't have any ideas at the moment.
Edit: To be more specific on the 0_download_json edits:
Replace "resource_code = '/'.join([resource_directory[-4:][i:i+2] for i in range(0, len(resource_directory[-4:]), 2)])" with "resource_code = '/'.join([resource_directory[-6:][i:i+3] for i in range(0, len(resource_directory[-6:]), 3)])" for lines 228, 333, and 427 [-4 is replaced by -6, 2 is replaced by 3]
Replace "for y in xrange(250):" with for "y in xrange(300):" for line 501 [250 is replaced by 300]
Replace "for idx in ((0, 1), (0.011, 35), (0.216, 6), (2, 10), (5, 50), (6, 200), (9.05, 10), (9.2, 20)):" with "for idx in ((0, 1), (0.011, 35), (0.216, 6), (2, 10), (5, 50), (6, 200), (9.05, 10), (9.2, 20), (9.51, 6)):" for line 513 [(9.51, 6) combined with the eidolon ID append command leads to 9511, 9512, 9513, 9514, 9515, and 9516, which are the Machine Beast eidolons' summon_id values, that I found by using them in battle with the Dev Tools open]
On my end currently I'm using the 0_download_json that you posted prior so I'm assuming that these edits are already in place. Currently I did not see any of the ayakashi rumble character scenes.
The error logs aren't that different: you have some Machine Beast eidolon files that didn't download during 1_download_assets, doing that step multiple times might help. I always do it at least twice for clean installs of both the Nutaku and DMM players. I have some errors that you don't relating to downloading extra json files that don't have assets due to experimenting with 0_download_json. I'm worried that one of my setups from before the uploaded edited scripts is what got me the files. Is there anyone here that have gotten the edited scripts to work?