observer effect
termops culturenetworking
When the act of measuring changes the behaviour being measured, so the fault disappears while you are watching for it.
Enabling debug logging slows a process just enough that a race no longer loses; attaching a capture changes buffering. The effect is not a nuisance to be worked around - it is a finding. A fault that vanishes under observation is telling you it depends on timing, which narrows the search considerably.
Also known as: heisenbug, probe effect