Mitsubishi Electric MELSEC iQ-R Series Programming Manual page 88

Precautions
For a program that uses functions, do not directly connect the return value of a function and an input variable of another
function, but connect a variable element between them.
Ex.
When the variable element (1) is connected between the return value and input variable
Connecting the return value of a function and the input variable of another function directly may lead an execution order to an
unintended one.
Ex.
An unintended execution order
Since both the output variable (3) that comes from another program element and the return value (2) of the program element arranged on the left are connected
as inputs of the program element arranged on the right, the execution order has changed.
7 FBD/LD
86
7.2 Program Execution Order
(1)
(3)
(2)