intermittent running

Hi all, I bought a Gain D30 in Sept.19, absolutely revolutionised my cycling, bringing a commute from home to work into range (17.5 hilly miles each way). However, I've had problems with the power dropping out occasionally and the bike having been back to the shop twice has now been replaced...

Today my wife's Anggun begun "cutting out." The motor will run for a moment then shut off then restart. The cycle takes 2.5 to 3 seconds. It happens in all gears at any speed. The battery has been charging fine and was fully charged at the time. The electronic display stays on as normal...