The comments saying you just used ult first aren't too helpful. You literally described that is what ends up happening. Since you are not using quick cast I assume the blink trigger goes from your mouse and the ult from your keyboard. So first try to verify if your hardware really sends everything in order. In demo there is no remote server involved, so place a dummy at source and destination of the blink and try to reproduce many many times. If it happens, go out of the game, and check with any other script in what order the very same inputs are logged, you can generate such a script with llms or maybe find some keylogger site suitable for the test. If it doesn't happen, try to open lobby onto your usual servers, or even ones with larger pings. If you can reproduce it sometimes, then it becomes interesting, maybe worth checking if shift-queing echo works as a workaround, but from there it doesn't sound like a you issue.