This does not make sense. If the filter roller backs up water the ato will trigger and overfill. Then in an hour the reefmat rolls. Now the water that was backed up is back in the sump and your water level is high. That water will then evaporate back out and you are at your original salinity. This would just repeat over and over.
I think something else is causing your salinity change.
I think something else is causing your salinity change.