My first guess would be there is too high a concentration of template DNA in the "abnormal" reactions. Did you standardize your template concentrations using a nanodrop?

Yes, we did Nanodrop and the concentrations should be the same.

To me it also looks like a too high template concentration. Have you tried doing a dilution of your sample. Looking at your curves i would assume you should try diluting by a factor of 100 to 1000.

I would be very happy if it is like you said but doubt it because we were detecting plasma miRNAs which are usually low