The monitor did not detect changes in estrogen or LH during this cycle. There are a number of possible reasons for this, e.g. a test may have been missed or not done correctly, or you may not have ovulated this cycle. It may also be that you did not set a new cycle. Remember that if your period starts then you will need to set a new cycle each time so the monitor knows a new cycle has started.
If you only see Low for 3 cycles you should see your doctor.