Nodes' labels are not showing in the preview and in the pdf

[pllchr]

Dear Everybody,
I am trying to draw a network using Geo Layout.
I am having troubles in visualising the labels in the preview and once I print the graph. I looked for solutions on this forum and online and tried various solutions, but none seems to help. I tried to use the same data but without layouts, same problem arise.

These are some screenshots that might help to understand the case:
The graph itself allows me to see the labels

Data seem to show all the labels in their place

Finally, I thicked them in the preview setting... but they are not there in the preview.

Any suggestion?
Thanks a lot
Chiara