This explains how to achieve a standard IF-THEN-ELSE style flow control so that it behaves the same way as you would expect if you had drawn a normal flowchart. I just found this out so I wanted to share it as soon as possible so the explanation is very much straight to the point, so I hope it is still useful.
Here is another blog that I found after writing my own that describes the same thing.
The aim: We have a simple flow where we want to run A and C always, but if a certain condition (i.e. User:Id == 1) is true then we want to run B before C. This "apparently" simple sequence is shown below. When we run the flow below with User::Id == 1 then A runs, then B and then C, so all is fine so far. However, when we run with User:Id == 0 then A runs but C will never run because it requires B to run with success as well.
The problem: With the default connectors, the condition for C to run is a logical AND of the constraints/conditions of its two input connectors. When you edit one of the connectors connecting to C you will see in the Multiple Constraints section that "Logical AND" is selected. This is the problem that prevents C from running if B doesn't run as well.
The solution: Select the "Logical OR" option so that C will run if either of its input connectors conditions/expressions are true. This will turn both the connectors joining to C into dotted lines as shown in the figure below.
Hope this helps!
By the way. I found another solution here that uses Sequence Containers.
