Instinct Solar Swim Charts stop at about 40 mins

I am having issues with my Instinct Solar only showing some of my swim session on the graphs. It will record for an hour for my swim fine which shows up on Strava as a hour. It shows an hour on connect, but when I look at the graphs, Pace, Stroke, SWOLF, it only records (or shows data) for about 40 mins.
I have tried on/off, reseting and hard resetting but this makes no difference, also tried unsparing with phone and re pairing again, no difference. All software is also unto date.

If I use my old Forerunner 920XT the graphs show fine, so I think it is to do with my Instinct Solar rather than my connect account.

Any ideas?