App not recording full map!

My watch has randomly stopped recording the full map of my activities. 

I’ve had my Vivosmart 5 for about a month now and it has been fine, but for the last few walks it will continue to track the distance and speed but when it produces the map at the end, half the journey is missing. 

GPS stays connected the whole time and I’m not walking anywhere obscure that could cause the signal to terminate. 

Anyone else had these issues?