The following change introduces new disconnect reasons that the WiFi service may return (as opposed to defaulting to the out-of-range reason):
https://chromium-review.googlesource.com/c/aosp/platform/system/connectivity/shill/+/1105397

The corresponding disconnect reason strings sent over DBus are added in this CL:
https://chromium-review.googlesource.com/c/chromiumos/platform/system_api/+/1105395

The question now is, what changes to the UI, if any, should occur because of these CLs?