I think that when acting as the stalker, Yakumo speaks a lot more informally and gruffly, whereas at work he’s the epitome of professionalism and kindness. The image gap is a bit much, probably. Also, they don’t seem super close at work tbh, friendly but not friends. It’d make sense for him to not recognize based on voice alone, esp since that personality switch is pretty big. Also Yakumo works at the same place and often helps with the documents right? If he does all the housework AND have sex, doesn’t that mean he only spends his sleeping hours at home??? I’d understand if MC automatically disqualified him on that alone
How does the uke not recognize the voice? Heck, Yakumo even talked so much. Surely there’d be similarities like choice of words or inflections and stuff… perhaps Uke was blinded by/ or all he thought was the good food, care, and sex that to hell with the identity? Hmmm