You should find this program and disable clearing of Planner 5D app cache (usually antiviruses, storage cleanup and similar apps do this).
If after doing this You are still seeing this issue, please check if it is really disabled:
#1 Launch Planner 5D application;
#2 Press question icon on toolbar and a dialog will popup;
#3 Press on About tab;
#4 Scroll down till You see section "Installation information";
#5 Check date "Cache": it is when last time cache was cleared - if it is recent time, this is most likely due to some app clearing cache;
#6 If dates that You see in "Cache" and "Launches" are the same, please contact our support.