Term or phrase describing action occuring when not watching

I am an IT professional. More specifically in automation. I am looking for a term or phrase that describes the event when either:

a. you are watching something closely and the issue doesn't occur

or

b. you are not watching something at all and the issue does occur

A watched pot never boils
Something you are waiting for will not happen while you are concentrating on it.

For a single-word adjective, consider stealth. Particularly during the last government, we Brits got used to usages like stealth taxes, where the general idea is you never actually see the money going.

The common catch-all term is Murphy's Law. In IT context specifically, there's the more specific term Heisenbug.

Heisenbug is a good term if this happens software, but if you're looking at something more mechanical, you might say that this is (or is the result of) a gremlin.

The simple term for any bug that only happens when it feels like happening is "intermittent".

If you can prove that the act of observing or not observing really does affect whether it happens, it's time to investigate things like timing dependencies, threadsafety, and so on. I have indeed heard "Heisenbug" used in the past to refer to this class of problems, but at best it's a jargonish description of a broad class of bugs with symptoms that are similar in this one way.