Feedback from Phonak:
First the change is an Update and not a new Version therefore reversion to the old one is not possible.
Secondly there is an IPhone issue regarding Autosense:
"the App reverting back to Autosense when you had put it into a custom programme; the older version of the app would not ’stick’ in the designated programme, it used to jump back into Autosense. Phonak have fixed this for the most part, however they are having some problems with iPhones - if you have the ’sounds and haptics’ switched on in your settings (that is what makes the sounds in your phone such as keyboard clicks, this setting is also responsible for the ‘lock sound’ you hear when you turn your phone off) they have found that when an iPhone makes the ‘lock; sound, it puts the iPhone into streaming mode and it reverts back to Autosense - so if this is happening they suggest turning off ’sounds and haptics’ in your settings. This way you can ensure that your hearing aids ’stick’ in the programme you have chosen. "
Personally I find NOT automatically reverting to Autosense a bigger issue that sticking with a setting.