Sorry if this was solved or not,
Curious, if your game folder was on an external drive, and what os were you running.
I had the same issue just recently and we determined that it was due to being on an external drive, which caused the problem. Once I moved it from my external to the internal drive on my mac, the soundbank generated fine.
Maybe something for the AudioKinetic guys to look into unless it has been fixed. This was running Mac Mojave, with an external ssd drive, and Wwise 2019.2.8
Thought I would mention it,