Can you make the same request in postman or insomnia and return full result?
A thing that I see is that OpportynityLineItems, the first item seem to be named “Projects OpportunityLineItems” record while the second is just named Projects record. And I’m not sure what you hide in red in the last screenshot. But if this is dynmically created, you will get issue because the field will always be different.
What I believe is that the OpportunityLineItems record doesn’t return what is set on the API Connector (first screenshot) and return what you see with Projects record - 2. Because the name is different, it doesn’t appear.
It’s hard to be sure what is the issue exactly without playing with it, but I think that you can start from that and check if this may explain your situation.