Frozen screen and route switch

Tried tempus fugit for the first time this morning as I wanted an easy flat ride. Half way through after giving a ride on the screen froze. Couldn’t get it back. Exited the app and re-entered. On doing so I was asked if I wanted to join the previous activity which I said yes to with a sense of relief. Then dismayed to find I had been transported to Watopia flat route! Any ideas? There was no drop in the internet connection Latest ipad with latest ios.