Cue Master sound spills into Cue Ch1/Ch2

I am using DDJ-FLX4. Cue Master sound spills into Cue Ch1/Ch2 even if it is not highlighted. The effect is that you could hardly hear Ch1/Ch2 when cueing. This happens when I'm about more than 30mins into a continuous mix. I would have to restart Rekordbox (7.1.1) to fix the issue. My Laptop is Asus Zenbook i7-8565U CPU@1.99GHz, 16GB RAM. Please help fix this bug asap.