Heisenbug
Also: observer-sensitive bug
A defect that changes or disappears when attempts to observe it alter timing or state.
Logging, breakpoints, probes, optimization, and memory layout can perturb races, electrical loading, and deadlines.
Example Adding serial prints hides a missed-deadline race by slowing both tasks.
Common misconception Intermittence does not make the bug imaginary; observation itself may be an input.