My drive is still failing to update. When I try to update it is showing the available firmware version as 22.5, not 12.3. See the screenshots below. I am on SSD Toolbox version 1.2.5.7 and have restarted. Even tried uninstalling and reinstalling SSD Toolbox and restarting again. No change.
Update 10/10/2019: Just wanted to let you know, I tried again today and the update to 12.3 went fine. It was probably due to the caching issue "Corsair Kevin" mentioned below. Unfortunately I didn't see that post till just now. But it looks like the caching issue resolved itself over time. All is good now. Thank you!