Hi @fallenzone
I haven’t met with such problem during the verification, but I assume this nonce verification message will not thrown by Google, but most likely by your WordPress site. So you will probably receive the same message when you try to verify other providers like Facebook or Twitter.
I am not really sure, but the problem is maybe caused by a third party plugin, probably a caching or security plugin. So I would suggest doing a plugin / theme conflict test first. For this you should disable all other plugins except Nextend Social Login and check if the verification works fine. If it does, then you could start enabling the plugins one by one or in small groups and you need to check the verification each time.
Once the problem occurs again, you managed to find the plugin that causes the nonce problem.
Best regards,
Laszlo.