Hi @stefano2
We haven’t received feedback about such problem, yet. But to avoid problems when some of our files may missing from your server, could you try deleting your current Nextend Social Login installation in your plugins list ( don’t worry if you have any configurations, those will stay fine ) and then install the plugin again from the WordPress Plugin Directory ( WordPress > Plugins > Add new > search for Nextend Social Login).
If the problem still occurs even after the re-installation is finished then please rather open a support ticket at:
and we will help you finding the cause of the problem!
Best regards,
Laszlo.