Error message "can't merge FlowVariable Stacks". How to handle?

I want to use the parameter optimization loop to impove the accuracy of results and get an error message “can’t merge FlowVariable Stacks”. How could I resolve the issue?
Thanks in advance!

Hi @vivatrone

With this screenshot (just of small or a big part of your wf?) its hard to tell what is (not?) happening. But this probably has something to do with the loops you use. Perhaps a loop is not properly closed. Or are they not nested properly. Or there is conflict with flowvariabls coming from the X-Partioner and the Parameter Optimization Loop Start.
A shot in the dark: bring the inner loop(s) (your screenshot) together into a component.

gr. Hans