Wondering if anyone else has run into the same problem that Im having?

I made a basic potato vodka by pealing and mashing 50LB of generic bulk bough potatos. I added about 20LB of white sugar. Steeped to convert starch to sugar, pitch yeast, distilled, ect.

I came out with a wonderful neutral semi sweet tasting spirit. But, after adding distilled H20 to bring it down. It developed a banana taste/smell.

Can anyone explain what Im doing wrong? Or has anyone had this problem?