Back in ye olde days, when the world was black & white and the coal fuelled industrial revolution was burgeoning, I used to be a web dev. I had so many ridiculous ways suggested/demanded of me to auto-complete addresses.

You'd have the Royal Mail's PAF, an API you'd have to pay a substantial amount of money for, that was usually the most accurate. You'd have 3rd party APIs that varied in accuracy (I suspect that's where your particular mess arose), and in one special case I had a company that didn't want to pay for API access, so instead decided they'd collate everyone's responses and just offer autocomplete per-address-field which lead to 6,000,000 misspellings of the same place name, and 12 tonnes of junk data from folk who didn't want to enter an address.