Reliability scheduled api on a list

Is it normal that if I set the interval of a scheduled api workflow on a list to low, (in my case problems rise under 40 seconds) workflows will succeed complete or uncomplete without making an error in the log?

In my workflow I need to add the item to several lists. I am testing with a list of 9 entries. In some cases only 6 of the 9 entries are listed.

What I don’t understand is when I set the parameters right, how can a workflow “forget” to add 3 of the 9 items to a list.

The flow itself is correct and when I set the interval on 60 seconds I do not get any problems. But this will mean I have to ask a new user to come back after an hour!

Can you tell if you have similar experiences?