Edge 130 Plus elevation accuracy is poor following switch off and on in mid ride.

Having been delighted with my Edge 130 I upgraded to an Edge 130 Plus.  I noticed a problem, namely that occasionally it would stop updating elevation, both in real time and on the final data.  OK, I can correct height online but it's dispiriting slogging up a 100m 12% gradient to be told that you have gained no height and it's flat.

I investigated further and discovered that the problem ALWAYS occurs after switching off the device mid-ride, then switching back on.  I carried out an experiment.

With the Edge 130 and 130Plus recording I did a quick up and down ride.  Both devices were accurate, and consistent with each other.  I switched both off and on again and repeated the up-and-down ride.  The 130 gave a similar result to the first lap, but the 130Plus elevation started to lag, only updating after a minute or so.  See graph below.  The Edge130Plus is the red line


I showed this data to Garmin Tech Support who agreed that there was a problem and agreed to replace it with a refurbished unit, which arrived yesterday.  And this one has EXACLTY the same problem.  See graph below.  The unit takes more than a minute to update elevation (on longer rides I've known it to fail to update for many minutes.

So now I await Garmin's response.  I wonder whether anyone else has had this problem?