Isomerization of pyrethroids

lambda-Cyhalothrin as others alpha-cyano-pyrethroids are analysed by
GC in pesticide analysis.
They have an isomerization to diasteromers because I evidence extra
peaks in chromatograms. Isomerization is described in basic pH but I
dont include a basic step in my procedure.

Why may be caused the isomerization?

I heard abuot reactions with the active sites of the liner but is not
very clear for me.
.