Recommendation on firmware

[boe]

Hello,

I'm seeing someone today who has a 6700 - for some reason it isn't able to sync even though other people at their office can - they have the correct time and date but it says the cert isn't valid. I thought maybe it might be the firmware since I haven't updated it in a while. What firmware would you recommend AKU 3.5 from august or something else?

Thanks