As I understand it you should got no more than one “immediate succession” of a particular job. Of course if you have 4 different jobs all of which missed their scheduled start time you’d likely see 4 “immediate succession” runs…
Here’s a description of how the schedule works with the most salient line being "Duplicati will first check if it is already in the queue, and if so, just not put it in there". Please let us know if you’re not seeing this in action.