Yeah, I read through those threads myself at the time and tried everything suggested, but to no avail.
After Monzo Support said there was nothing they could do at their end, I just asked them outright who provided their address lookup. The support rep refused to name them, saying Monzo don’t publicly disclose their suppliers.
I’d be happy to share what I did to work around it, but I’m not quite sure where I stand with disclosing it on Monzo’s own forums — especially as (surprisingly) there are no Google results to suggest this company works with Monzo, either.
For what it’s worth… the supplier’s address data has nothing whatsoever to do with Royal Mail. It’s an entirely proprietary dataset, from a company you’ve definitely heard of…