This is a quite normal behavior of the macro bike computer.  When you take a break the sensor goes into sleep mode after a while. It wakes up again when moving the bike but the head unit won't find it directly. The automatic searching takes place every 6 minutes (for saving energy it can't be more often). To avoid this gap you can do a manual searching (press the lower and the middle button at the same time). The sensor will be detected directly and speed will be shown on your macro computer immediately.