Consider that in a LLM, language inputs are tokenized and fed as inputs into the neural network, and connections in the network create output sequences that are not just syntactically correct (trivial) or form semantically plausible sentences (early transformers did this). LLM output sequences follow the deep patterns of language which include sometjhing that resembles reasoning as the model has learnt from its training data.
LLMs seem to fall short because they often fail at truly abstract reasoning tasks that humans find easy. If trained properly, LLMs can develop advanced representations of logical systems that will surely outpace what humans can do in terms of raw reasoning.
However, human mathematicians have not even unified around constructive mathematics as a must for the study of mathematics. This reveals that even highly evolved mathematical disciplines rely on objects whose characteristics do not lend themselves to full logical scrutiny and are in a way socially constructed and effectively hard to audit.
While notation in mathematics is incredible technology it is also a highly limiting factor that suffers major tradeoffs. Humans struggle to invent new notation fast enough and to discard outdated notation fast enough. If we do see an AI-powered boom in mathematics, I suspect our notion of notation and the fluidity we demand from it will change dramatically.