Qingping Air Monitor and slightly high (yellow) tVOC

i have this device from some days https://www.qingping.co/air-monitor/overview , using it in my room i see that tvoc parameter always go to yellow after 10-15 minutes i close my window for put in fresh air

i don't use chemical or cleaning products, i don't have in my room nothing that can make higher that parameter, usually is always over 1.000 mg/m3 and if i don't open a window in a couple of hour it can arrive at 1700 mg/m3, in the night it can arrive to 2500 mg/m3 (i don't keep window open at night)

don't understand why this happen, i read some other threads in this reddit of users that have this device and are experience strange high tvoc , what do you think? is a problem with this device or not?

https://www.reddit.com/r/AirQuality/comments/ylk3gl/high_tvoc_readings/

https://www.reddit.com/r/AirQuality/comments/zr4dcm/tvoc_1200_goes_to_800_with_windows_open/

https://www.reddit.com/r/AirQuality/comments/ylk6wf/high_tvoc_readings/