Hello @rosspyres,
how do you control which columns are converted in the first node? And also what are you really doing here? From Date&Time to String and back? Maybe there is a different way to deal with it?
Described behavior can be due to Enforce exclusion/inclusion configuration in second node. If you have Enforce exclusion option and empty column list you’ll always get all columns converted regardless of flow variable. I found this topic where I (maybe) explained it a bit more with couple of other ideas/remarks:
Br,
Ivan