That is funny that the index works. You're right, this does look more like that other issue.
+1 to Parker's issue. I can no longer get sound on legacy versions. It looks like they might have set the S3 bucket permissions to private, or something.
I can confirm this issue on a Titan X Pascal, with no mods and all settings on max, save mipmapping, which is off.
Uploaded an additional logfile of this reproduced with 1.5.2 (occurs with older versions as well). Log is truncated due to me shutting game down before it tried to get all assets.