Forerunner 45 displays 5568km and contnual beeping after locating GPS for activity start and will not record anything

Forerunner 45 displays 5568km and contnual beeping after locating GPS for activity start and will not record anything. This feature did work, phone new in April. All updates are up to date. This weekend the watch, takes a while to locate GPS and then flashes up a 6658.6km message on screen and beeps continually and will not record any activity. Any advice much appreciated.