EEG Quality (EQ) has been built to give you an easy way to assess whether you are recording high-quality brain signals or not. Basically, it is a scoring system for the quality of the signal in each sensor. It is not meant to stay at 100% all the time. If you have a lot of movement (artefact) this will affect the EEG quality, when you have other wireless /bluetooth devices near the headset, this can also cause noise and affect the EEG quality.
I have also had this experience with my EPOC X headset. Try to keep still for about 10 seconds and you will see that the EEG quality score will remain good, because there not so many movements. But if you start moving your arms, like to adjust headset or type, it will drop the again. If you can have someone help with working the computer so the wearer of the headset can avoid moving. You can still do your recording despite the fluctuating EEG Quality score. You just need to account for the artefacts and noise when processing your data.