I ran Kodi 21, on my VU+ Duo 2, using OpenBh 5.4, but quickly did a fresh installation, and reverted back to Open Bh 5.3, Kodi 20, as my addons didn't work, in Kodi 21. I will try OpenBh 5.4, in the near future, when I gave time, to see if my favourite addon, has been updated for Kodi 21.
You might have to delete all your Kodi files, off your hard drive, and re-install them. Deleting them will cause you to lose all your addons, favourites, and settings.
You can delete them using Filezilla, just connect, using root, your receivers IP Address, and password.
You then need to alter the settings, to show hidden files. Go to the Server tab, top right, and tick the Force showing hidden files.
You should then find the .kodi folder in Media, hdd.
