CBE monitor bad test sticks

I'm using the clearblue easy fertility monitor. I have had 4 sticks that seemed to have issues. When I looked at them after removal from the monitor, the dye was still pooled at the end. This caused the monitor to read high (2 sticks) or peak (2 sticks) erroneously. All of the sticks I've used have been used in the same manner (15 second dip in a cup). Is this a problem with a certain batch of sticks?