Korg Kross 2 - Pitches reversed or not sounding

Keyboard worked great for 4-5 years but this week the notes started playing backwards (high pitches on the left, low pitches on the right). Three keys on the left side don't sound (Bb2-C3). And an octave of keys on the right side (C#6-B6) don't sound.

Each time I turn the keyboard on, it says "Now writing to internal memory" for a few seconds. Then it displays the message "System warning: The internal memory has been corrupted, likely due to an interruption of power while the system was writing/saving data. This has been repaired and the affected Bank has been initialized."

I can't think of when it would have lost power while writing to internal memory. I almost never save anything.

In an attempt to resolve the issue, I upgraded to the latest firmware 1.22 (previously on 1.21). Per the "Restoring the factories settings" section of the manual, I tried "Loading the preloaded data" and "Initializing the system". After each attempt, I got the same results.

Any ideas?