The DNA sample has an unknown concentration, but it should be around 21 ng/µL according to a nanodrop measurement. All of my other samples produce a decent looking curve that plateaus afrter a few cycles. The sample is diluted in a 50 mM Tris-HCl buffer, pH 8,0 containing 150 mM NaCl, 1,5 mM MgCl2 and 5% BSA (m/v). I have never seen this pattern before using these reagents. I read that the problem could be my sample evaporating, but the vials where still closed when they were taken out of the machine and there seems to be no loss of volume. I am very curious to know what could have caused these abnormal results.