Common reasons for bugs in release version not present in debug mode

What are the typical reasons for bugs and abnormal program behavior that manifest themselves only in release compilation mode but which do not occur when in debug mode?

Many times, in debug mode in C++ all variables are null initialized, whereas the same does not happen in release mode unless explicitly stated.

Check for any debug macros and uninitialized variables

Does your program uses threading, then optimization can also cause some issues in release mode.

Also check for all exceptions, for example not directly related to release mode but sometime we just ignore some critical exceptions, like mem access violation in VC++, but the same can be a issue at least in other OS like Linux, Solaris. Ideally your program should not catch such critical exceptions like accessing a NULL pointer.

A common pitfall is using an expression with side effect inside an ASSERT.