Why do address forms fail more on mobile?
Because the two things that make an address hard to type are worse on a phone. The screen is small, so the form scrolls and the customer loses their place. The keyboard is a touch target, so characters get missed, doubled and transposed. Autocorrect then rewrites street names it does not recognise as words.
A desktop user with a physical keyboard hits none of that. The same form converts worse on mobile for reasons that have nothing to do with the customer's intent.
What should you change?
The customer types a few characters and taps a validated address. Nothing is typed in full, so nothing is mistyped
Larger inputs and buttons, fewer fields on screen at once and no scrolling back to check what was entered
Set autocorrect="off" and autocapitalize="off" on address inputs, so a UK thoroughfare is not rewritten into an English word
How does address autocomplete work on a phone?
The customer starts typing and picks from a list of real addresses. Address Finder attaches to your existing address inputs and fills them from the selection, so the fields your form already submits receive validated values. Fuzzy matching covers the typos that happen before the selection, which on a touch keyboard is most of them.
Which is better on mobile, postcode lookup or address finder?
Address finder, in most cases. A postcode lookup asks for a full postcode before it returns anything, and a mistyped postcode returns nothing at all. An address finder returns suggestions from the first few characters, so the customer sees progress immediately. The postcode lookup and address finder comparison sets out where each one still wins.