I have experienced something similar this year - it's not something I've seen before.
Everyday it can change. One day my client is number 5 for "keyword" - the next day it has gone.
This has been happening for about 3 months now.
I am putting faith in Google eventually settling down and keeping them on the first page. It is a very difficult one to explain though and I don't have the answers.
This is not about having a better SEO strategy - this is about something I'm calling GHOST RANKINGS
Anyone else seen this .. and what happened?
P.S I'm am incognito when I check. I also track it in MOZ rankings. I have also got people to check from different locations - this is not the reason!