It looks like I was unlucky and that my Osmo+ unit is defective:

• The wifi connects to my phone (iPhone 6 Plus) but the DJI GO app loses the image intermittently. In some cases, I have had to fidget with the connection for >30 minutes before getting it to work… and then it still intermittently drops out. (Have tried resets, firmware upgrades, removing phone case, turning off all wifi in filming location, switching wifi channel, using a different phone…)
• Worse, the audio is out of sync on some clips, in what appears to be completely random ways (no way to know which clip will be affected). You can see this problem here: https://www.dropbox.com/s/0fo2g3ta343gz84/audio%20sync%20issue.mp4.mov?dl=0
  

DJI Tech support says that on the basis of the video above they should be able to diagnose the problem. However, repairs currently take more than 15 days… So I'm taking this unit back to the shop where I bought it (local store that had it in stock!) and getting them to replace it with a new unit.

From a few Google searches, the failure or defect rates on the Osmo+ seem to be significant enough that one can find a number of testimonies relating the same problems…

I have a lot of videos with the same Problem, how can i fix that?

kalunga Posted at 2017-7-16 03:50
I have a lot of videos with the same Problem, how can i fix that?

Would you please try the following method to refresh the firmware to see if the problem persists?
Download the firmware to the root directory of SD cad;
Before powering on, keep pressing the Trigger and Record button simultaneously, then pull the Power Switch down for about 5 second until the right LED blinks red and green
The OSMO will detect the firmware and begin updating;
The update is complete when the LED displays solid green.

Did you send the device to your dealer and how is going? We are sorry for the unpleasant experience with our product. Please keep us updated.

DJI Mindy Posted at 2017-7-16 20:23
Did you send the device to your dealer and how is going? We are sorry for the unpleasant experience with our product. Please keep us updated.

Got a replacement that is working so far.

Also I was using Sandisk Ultra memory card and have switched to Sandisk Extreme.

So far, so good.

kalunga Posted at 2017-7-16 03:50
I have a lot of videos with the same Problem, how can i fix that?

From what I've been able to find online, you may need a faster memory card to prevent the audio sync problem. At least until DJI releases an updated firmware…

DJIFanInGeneva Posted at 2017-7-17 00:03
Got a replacement that is working so far.

Also I was using Sandisk Ultra memory card and have switched to Sandisk Extreme.

It's good to know and hope you have good time on shooting.