1. It looks as your brine pipe may be loose. Please check if the nuts on white hose and grey tube are not loose. If the nuts are loose then no water is sucked out of the brine tank. So the new water is added during REFILL to the remaining water level and brine tank overflows.
2. If the nuts are tight please check the injectors. If there is dirt in the injector then it can overflow too because the unit can fill up the Brine tank instead of sucking water out. Please check this English video from time 1:50. https://www.youtube.com/watch?v=TCLdjSeDzog