"Heisenbug"
yeah, those are annoying...
like, bug which is annoyingly hard to recreate and occurs rarely, may appear only when not run in a debugger, or when the code is stopped/single-stepped there is no evidence of the bug's existence... (ex: program runs with a bug, set a break-point, single-step, and everything works as intended...).
may sometimes be due to "spooky action at a distance", like (off somewhere in some distant part of the program) instead of writing "foo[x*y+z]=...;" one wrote "foo[x*y*z]=...;" which may otherwise go largely unnoticed if it fails to land on an unused memory address (may be very common for programs where most of the address space is in-use).
may be also be called "dude, where's my RAM?" if it also results in an intermittent memory leak.