PCR and large-scale PCR
I made the large-scale in a falcon tube and then moved the mixture to PCR tubes each containing 50 μL, so the PCR conditions should be the same as the single PCR amplification

If all reagent concentrations and cycling conditions are the same, I suspect that you did not sufficiently mix your large-volume reaction prior to dispensing as 50 μL aliquots.

It should be mentioned that the single PCR was performed in the summer, and the large-scale was performed now

If you were using the same polymerase and primer stocks for the small- and large-volume reactions, were the stocks properly stored in the interim? Recombinant DNA polymerases in glycerol buffers have shelf lives of months to years depending on the supplier specifications and storage conditions, though you should expect some decreased activity after several months.