Service Desk 7.6
In Process Designer, when I add the grey Assignment arrow or select the "Add Assignment" action to add to my process I will not get the relevant Assignment window up. I will instead get the default Incident / Change / Problem / Request window up.
This is happening if you have a windowless action called: "Assign"
Process Designer will confuse this action with the normal "Add Assignment" action and therefore add the Assign action to the process instead.
Rename your windowless action to anything else but "Assign", for example "Assign Incident"
This has been fixed in 7.6.1