chat gtp said that [address reuse] could be a reason for issues.
I wouldn’t rely on Chat GPT because Chat GPT also says that 2+2=5 and doesn’t understand what the heck it is doing. Chat GPT is a language model that takes any old nonsense and converts it to a superficially plausible grammatical paragraph or two.
As https://openai.com/blog/chatgpt says
ChatGPT sometimes writes plausible-sounding but incorrect or nonsensical answers.
I suspect that “sometimes” may mean “often”.
Address reuse was the norm when Bitcoin Core was first written, I am sure that address reuse does not cause the issues you describe.
How can I get bitcoin core to display [the balance I expect] properly?
I would make sure Bitcoin Core is fully synchronised. There is an icon at bottom right of its window that tells you if it is synchronised or catching up etc.
I would check that the transaction corresponding to the missing amount is a confirmed transaction (e.g. using a blockchain explorer)
