Thanks for the additional information.
This is an example of query that is very generic. As a result, it is not unusual that the GPT’s responses lack specificity and comprehensiveness. If you are looking to get more targeted responses, then you need to implement an approach where the model requests the user to further detail the question if the initial query is too broad.
Alternatively, if you expect similar questions across your user base you could also change the way you organize the knowledge file and instead include in the file question-answer pairs.
I can’t speak much to the fact why the GPT’s behaviour might have changed. Several users have been reporting different behaviours after GPTs were migrated to the new gpt-40 model. Every model responds (slightly) differently to instructions and you might need to spend some time calibrating your existing instructions to fully get it to work again.