What is this smell

[nokia3210567]

Just moved into a house and the lobby has a weird smell. Kinda like baby poo?

Doesn't smell damp or mouldy imo, didn't smell this when we viewed the house back in March.

Any ideas?

Did the last owners have cats? I've had dead rodents hidden in very odd places that I've had to sniff out, in the past. Can sometimes be an acrid, almost sweet odour of decomposition. Not overwhelming because of the size but noticeable, certainly.

Not related to your situation but worth noting anyway; faulty/melting electrical cables can smell like cat pee.

Btw; I referred to cats because my cats would bring in the dead mice. I'm not insinuating there is a dead cat! Apologies!
Of course, rodents could have died by "natural causes" without cat assistance.

Could it be something in the carpet? Maybe they masked the odor with air fresheners or a bit of shake and vac so you didn’t notice. Maybe clean the carpet and get a good air flow going and see if it shifts it.