Two peak readings a week apart

After using my monitor for a few cycles, this cycle my monitor showed peak fertility on day 9 of testing. 

I then went for a transvaginal scan 10 days later & the sonographer advised my right ovary would be releasing an egg in the next couple of days. I used my advanced digital test the next day (as the monitor won't allow you to test again in the same cycle if peak has already happened) and it did indeed show a flashing smiley. I tested again the same evening with the advanced digital test and it moved to peak ovulation in line with what the sonographer saw on my scan. Is it possible the monitor gave me an incorrect reading on day 9?