Hi,
I am happy that pdf helped you in getting understanding about single ended to differential filter conversion.
First of all I am not able to view any of your uploaded images in large size. So it is very difficult for me to comment on what did you synthesized and what did you simulated in ADS.
1. Could you please update on filter specifications you are trying to meet and also upload images properly so that I can view them properly ?
2. What was your synthesis impedance ?
3. Yes, you can ignore the warning as it will look for ground node.
4. What tool are you using for synthesis ?
Please give some information as requested above so that I can help you better.
Cheers,
Antonio