I have replicated the set up I believe you have here - if you inspect the Flow variables you see flow variable “PortChoice” with value “PortChoice” (the name of the column you create, which is what the setting from your first screenshot does).
For some reason it actually keeps both branches active in this way, resulting in both branches being processed and resulting in duplicates in my Loop End
Compare this to this set up, where Table Row to Variable is used:
Variable has the correct value and only one branch is triggered.
Here is the workflow containing both options (top "yours”, bottom “my suggestion”)
IFSWITCH.knwf (70.1 KB)