I would calibrate the NanoVNA again with binding posts. I would use something like 30MHz-100MHz, 900MHz is surely too much. (Like others have said.) When the Vna asks "open" I would leave the binding posts empty, "short" mean shorted binding posts and "load" means a 50 ohms resistor(or two 100ohms in parallel).
Then I would check everything with capacitors. Values around 56pF are good, like 100pF and 10pF. Have you some coils too where you know the inductance. When all these show good values (+-tolerances), you'll know that everything works.
I have used crocodile clips up to 30MHz, your binding posts have shorter leads, so they should work with 50MHz. I have noticed that with crocodile clips, test leads matter a bit, your binding posts are better.
