–use-block-cache creates a block lookup cache in memory to avoid DB. An early test didn’t see much gain. Seems pretty far removed from passwords, but you can certainly try removing it to see if it helps that issue.
As a note on exporting to JSON, this won’t pick up global options from Settings, so look there, or instead do Export As Command-line or Commandline to get a better view of what your backup would actually be using.