Yeah, good times. I just recently had one that was a really strong misdirection, ended up being 2 simultaneous other, non related things that conspired to make it look convincingly like my code was not doing what it was supposed to. I even wrote tests to see if I had found a corner-case compiler bug or some broken library code. I was half way through opening an issue on the library when the real culprit became apparent. It was actually a subtle bug in the testing setup combined with me errantly defining a hardware interface on an ancient protocol as an HREG instead of an IREG, which just so happened to work fine until it created a callback loop inside the library through some kind of stack smashing or wayward pointer. I was really starting to doubt my sanity on this one.