Niby nic, ale pokazuje bardzo silny akcent na 'tego'. "THIS I do not have anymore". Like "Okay, so you asked for three things... I have this, I have this, but this I do not have anymore"...
Nie chodzi mi o to, że to wada systemu. Po prostu ta odpowiedź z jednej strony nie jest błędna, ale jest... trochę dziwna. W większości kontekstów brzmiałoby to dziwnie.
We can say that "ja" is almost always superfluous, but also always correct. As for "Tego już nie mam", the emphasis is really too strange and yeah, placing "Ja" explicitly makes it a bit more acceptable.
"I do not have it anymore" - a classic translator error is to confuse 'it' and 'this'. Without more context, such as a photo of the object, then 'this' indicates we do actually have it here.