What problem does this address?

When a navigation block is in a fallback state, it creates a draft wp_navigation CPT, once a user interacts with it. If this draft is not saved then, next time we load the block we load the fallback again, rather than the draft. This can lead to a situation where a user has multiple draft wp_navigation CPTs in their admin.

What is your proposed solution?

When the block is in a fallback state, we should delete draft wp_navigation CPTs, and create a new one with the latest fallback data, to avoid creating multiple useless drafts.