I guess no one knows the answer.
My router is the same. I have 1.21 firmware and the router replies that I have the latest version.
It appears to be a bug in the firmware.
Hi HighSierra,
Actually, it is not a bug. I am running the latest version or the same version as you are: 1.21
Firmware 1.21 is the last version from 1.00 to 1.21, where one can go back and forth without problems.
Once you install the later versions 1.3# and latest, you can't easily go back to version 1.21.
That's why, I haven't upgraded.