Mine is a simple off by one byte write causing a failure in a separate thread in proprietary barely related code on deinitialization of the library. It took yea

Mine is a simple off by one byte write causing a failure in a separate thread in proprietary barely related code on deinitialization of the library. It took years to find. Not even ASAN, valgrind and debug allocators helped. What did was a full audit including assembly. They had their own memory allocator and internal threads, the off by one corrupted an atomic flag... Since this is data dependent on a relatively cold path the issue did not appear that often. And less predictably because it was ARM. Note the multiple stacked undefined behaviors.