Hi Greg,
I confirmed the cause of the issue and the current solution.
This issue will be resolved when you configure one of these:
1. Disable “Block by country” at “Admin ajax/post” on “Validation target settings” of IP Geo Block
2. Select other than AJAX at “Load Popup using” on “Popup Loading Method” of WordPress PopUp
And currently, I’d like to recommend you to choose No.2 because of the long story.
Generally speaking, plugins and themes using ajax potentially have the same vulnerability as of Revolution Slider which was very famous for its impact to the web society in 2014.
You may be interested in the following articles.
https://www.ipgeoblock.com/article/why-so-vulnerable.html#file-inclusion
https://blog.sucuri.net/2014/09/slider-revolution-plugin-critical-vulnerability-being-exploited.html
https://www.wordfence.com/blog/2016/04/mossack-fonseca-breach-vulnerable-slider-revolution/
Even if you choose No.1, you site is still safe by means of filtering “Bad signatures in query” against the attacks targetted for the similar vulnerability of Rev Slider. But of cource, there’s other types of vulnerabilities via ajax.
I’ve been studing how to block malicious attacks against ajax served on public facing pages. And in the future, I’d like to propose the similar method of “Prevent Zero-day Exploit” to all my plugin users :).
Although I close this topic, I’m always opend to hear your voice!
Thanks.