OPK CLEARBLUE ADVANCED VS WONDFO

So I took a WONDFO opk it looked positive to me so I took a clearblue advanced opk that's supposed to show you, your 4 most fertile days. CLEARBLUE said negative 👎🏻. Which has me thinking why if the WONDFO looked positive to me then why wouldn't clear blue not even have a flashing smiley. I'm leaning towards the CLEARBLUE.  Has this happened to anyone and what was the out come.