Well, jumping off from some posts on the old forum, I managed to get it to work. In case anyone else has this problem, here are some of the steps I followed. 
  
- Tried a global parameter reset, nothing. 
- Tried the "hold down DOWN and power up, then load latest firmware". Didn't work. 
- Rolled back to 1.10. It worked, fixed the overdub problem. But when updating from 1.10 to 2.20 I got reboot cycle. 
- Basically, I loaded 1.10, then 1.43, then 2.02, then 2.20. Each step I had to go back and forth a couple times until it worked. 
- Now overdub works correctly in 2.20.