Word for count of undesirable events

TLDR: name for count of hiccups?

I'm trying to find a short¹ word for the count of undesirable events, up to some number of experiments, and tending to increase with the number of experiments as these undesirable things occur. The name should be usable for that count, and to name a function, in the math sense of that. A definition will be given, thus the word does not need to convey detail beyond undesirable. So far my best candidate is slack. Usage could be

• The average slack up to 1000 (experiments) for this device is 42
• The ratio of slack to experiment increases with temperature.
• The slack of a device is defined as the function that given N, returns it's average slack up to N (experiments).
• This technique leaves more slack than this other one.
• It goes without saying that the slack is non-negative, and a non-decreasing function of the number of experiments in an experimental campaign.

The word should be recognizable by an educated international audience with English as a second language. It's OK, even desirable, if the word is colloquial, as long as it's universally safe for work.

What about slack versus leeway, (updated: hiccup, mishap, though that's more for the event itself than for the count of it) ? Anything better?

Note: I rule our plain error or defect because they imply the device is defective, when slack is something resulting from a deliberate cost/benefit tradeoff.

¹ Update: I realize, late, that I need a diminutive, and that's why I want it to be short. What my slack counts really is integers that we want prime, but are not. The research field (number theory) I apply to actual devices (Smart Cards) treats integers with utmost respect. Thus calling them error, defect or failure would be offensive.