time warp?

[snowbird30ds]

I have a garmin 557xs plotter and both times across the thames estuary this week it has jumped back an hour for a big chunk of it and jumped back forward, only on the time display navigation was spot on, it's never done it before and both times was in the same vicinity, this is the first time I've crossed the estuary.
Have I time travelled and has anyone else found this glitch?
It was between kings channel and coming out of foulgers gat.

 

[ex-Gladys]

Have you updated the software? A few years back there was an issue with some of the Garmin Plotters of that generation with time handling...

 

[snowbird30ds]

I updated 2 years ago when it froze after a few hours and it's been good as gold since, just seems odd that it only happened in the same area.
Updating is the next plan.