There are several methods to enter restore mode for updates. Odd that this is not working, but maybe worth trying them all? Worst case, we can do a full factory-reset of the unit.
Anyway, the methods for entering restore mode are:
- press&hold down the left knob and footswitch for 5 seconds while powering on the unit
- on a regular boot, use the device menu system->start upgrade
- on a regular boot, use the settings on the webgui and click the button “start update mode”
if all of them fail, we can still force entering restore mode by booting over FEL. though this is considered advanced and is for linux only (it is what we use for testing without breaking/overwriting anything on the duo units)
Download download.moddevices.com/releases/modduo/tools/boot-fel-restore-mainline-debug.tar.gz and run the “boot-fel-restore.sh” script inside.
If the advanced option is not really an option (understandably for most users), factory-reset steps are described in Troubleshooting Reinstall Duo - MOD Wiki