Sorry for having kept my answer a bit (too) short. The problem occurs, if you do not have set any forced plugin settings for backup and restore. That's why adding the config keys help.
Background: The issue occurs only if a backup/restore job is being run by a cron runner that has run the recycle bin task before, because the recycle bin task unfortunately by mistake sets the mentioned configs to null, if they aren't set, which then makes the function get_config fail with the error you were seeing in the task logs.
A workaround is to set the configs I provided, because if they are already set, even if they are set to an empty array, they will not be set to null by the recycle bin task, so everything is running smoothly again.
Hope this makes you trust my suggestion for a workaround