If more than one join path leading from a workflow stage to other stages (or in a Multiple Branch behavior object)references the same object (for example a checkbox) you cannot use a Simple condition on any of the join paths.
Example: If the instance can move to three possible stages depending if either Checkbox A is checked, Checkbox B is checked, or if Checkbox A AND Checkbox B are checked. The conditions on the join paths must all use the formula editor and must read as follows:
1: Checkbox A is checked AND Checkbox B is not checked.
2: Checkbox B is checked AND Checkbox A is not checked.
3:Checkbox A is checked AND Checkbox B is checked.
If you use a Simple condition the workflow will not work properly.