I think that may be a limitation of the app when switching sync targets while e2ee is enabled. It takes the encryption status from the sync target, which in this case is new and thus with e2ee disabled, so it also ends up disabling it in devices. I will check and see how that can be improved
For it to work you need to enable it in one of the device (preferably on desktop because it's faster) and then sync again. Once that's done you may also need to sync your other devices