Yours is identical to mine for all intents and purposes except that I call my assist key directly from step 1 in my DPS keys. Are you pressing SHIFT+A to assist every time you need it? If so, try adding it to your dps rotation mapped key and see if it still fails. If it does NOT fail, then I suspect it has to do with the SHIFT modifier state getting intermittently screwed up, which means it probably isn't the game or any addons.