Hmm, I'm just getting really inconsistent results. Often it clearly does not behave according to the text file I uploaded to its knowledge, it just ignores it. And then when I remind it of this file, it will start a "Searching my knowledge" or "Analyzing" animation which can take ages.
Do you find that your GPT is always clearly aware of the documents you fed it?
Edit: I just looked at the first custom GPT I created and I uploaded a new document, and the UI indicates that the new document is part of its knowledge, while the old document is only available through Code Interpreter. I have no idea if something changed or if I did something wrong, but this perfectly explains where my misunderstanding came from.