Hi just thought I'd share my thoughts. 3 week old nokia 8... camera was working brilliantly a few days ago. today auto focus stopped working on rear camera in color or dual mode, but mono auto focuses perfectly. Front camera no problems.
Found the only resolution was to shake the phone with some volience (as much as I can without dropping it!), and voila! auto focus works. Sounds like similar issue to Jaunan Lopez original post.
Also downloaded another camera app, and same problem. So seems to be a hardware design issue, not software... but then why does auto focus always work on black and white mode? Presumably to do with the action of the twin lenses that comes into play in that mode??