GPX timestamp goes back in time

I'm developing a MS Access database application for processing and storage of all the data exported by my Gôrmin Nuvey 3490LMT, and by my late Gôrmin iQue 3600 (bought in 2003) and Gôrmin 45XL (1996). It derives all kind of metadata per track, it has graphs, and also an export function to show the processed data in QGIS.
No problem at all, until I tried to process a GPX of a trip in Germany, made 18-10-2015. It turned out that this GPX has a record in which the timestamp is 43 seconds earlier than the record before!

Time Lat Lon Speed (according to GPX)
09:24:25 49,7785250 10,0903030 98,8
09:24:46 49,7760170 10,0832070 98,8
09:25:06 49,7732610 10,0767390 98,8
09:24:23 (!) 49,7698490 10,0700000 98,8
09:24:43 49,7664340 10,0643300 98,8
09:25:04 49,7625770 10,0588040 98,8
09:25:34 49,7569480 10,0511890 98,8

This is the only time this happens in all my GPS data recorded in 20 years up to now (which comprises almost 2 million records).

What's is happening here?

Rgds

IF / FF/ HF

 

Good try, Nuvi-Nebie! Thanks.
But if we rearrange the records this way the differences in seconds combined with the distances from point to point lead to weird speeds. I was driving there with cruise control at 100 km/h.

Time Secdif Lat Lon Dist Spd
09:23:39 49,7829720 10,1066440
09:24:01 22 49,7810380 10,0986790 610 100
09:24:23 22 49,7698490 10,0700000 2404 393 (!)
09:24:25 2 49,7785250 10,0903030 1747 3144 (!)
09:24:43 22 49,7664340 10,0643300 2297 376 (!)
09:24:46 3 49,7760170 10,0832070 1723 2067 (!)
09:25:04 18 49,7625770 10,0588040 2301 460 (!)
09:25:06 2 49,7732610 10,0767390 1751 3151 (!)
09:25:34 30 49,7569480 10,0511890 2578 309 (!)
09:25:52 18 49,7537990 10,0462470 498 100
09:26:10 18 49,7509260 10,0409170 498 100

The cause of this sudden 43 seconds time leap into the past could be that my Nuvey's internal clock was running ahead by 43 seconds for some reason, and the GPS time corrected it. But I'm in doubt about that. I was using the unit every day and the trip in question started 1,5 hours earlier without any problem.

Maybe a big time leap in the whole GPS system? I doubt, since a short search on the internet gave me no message at all about such a thing on that day.

 

About the 30 seconds timing error: I do not think so. During those 30 seconds I drove 830 m (calculate the distance between two points), that is my speed was a calculated 99,6 km/h (0,83 * 3600 / 30). That corresponds with my recollection that I was driving with cruise control at 100 km/h.

That leaves us with the 43 seconds error. Even Gôrmins have errors sometimes.....

 

In my data of the last weeks I have discovered two more cases of this phenomenon. In one of them the time jumps almost two minutes back. I'm very surprised. What's going on? I'll try to contact Gôrmin about this.

 

Could be. However, apart from this rarely occurring phenomenon my Nuvey navigates happily and flawlessly all the time! So the timing error does not seem to affect the rest of the unit.