My 245 fails to record all of my swimming lengths and doesn't record some of my walks

I have set the 25m pool settings, do exactly what Garmin advises ie push off from the wall etc but it still fails to record all my lengths especially when swapping to the 'drill' setting it doesn't want to go back to my swim session ? 

When going for a walk or bike ride it sometimes just stops recording without warning and when I stop I see hasn't recorded any of my activity ?