Strength switches randomly to next exercise

I use the Strength activity for my workouts in the gym. Normally I switch to the next exercise by pressing the right top button manually and adjusting the number of repetitions and weights. Since a couple of weeks (maybe with an update) the next exercise is already starting during an exercise, without pressing the button. It looks quite random, so not after a certain time. This is very anoying, the exercises become a big mess on my watch. Anybody have an idea why my exercises switch automatically?