CVT fails when reaching 60mph
 

My cooper from 12/06 has had numerous transmission problems with finding a gear around 60 mph....it can not decide to up or down shift.... so the RPM just starts rise 3500 > I have had the problem on/off since I got the car in 2006 and how weird it might sound the problem often appears after a service check or a "software upgrade". So the BMW found that because of the cars ability to adapt to the driver a proff. mechanic need to do a "special" drive before handing it over. It usually works and no problem appears for apprx. 6 month and then we are back.
They are getting really tired of me and they say that everything is fine - but reading all the comment it seems that I´m heading towards a seriose problem. The car has now gone 50.000Miles
Any suggestions on how to fix the issue that seems to come and go as it please....

I'd say it sounds like a software issue and when the reflash it it goes away , I'd have no idea why it would go after 6 months though