I’m aware this is an old thread - but for anyone else with the same problem finding this… I’ve just had this issue suddenly crop up on a project… an unplayable delay on trying to record a guitar part. Searching for a solution I found these posts. It indeed turned out to be Steinberg’s own Multiband Compressor with I’d dropped on the Output bus last thing before doing a Mixdown on my previous session. So this is definitely worth checking if you have this problem suddenly occur. Cubase Pro 12.