I see, sometimes it will happened but sometime it’s fine. I think maybe it’s a small bug in NHP options framework, I’m planning to change the framework to Redux framework in the later version.
Sometimes, I change another browser to upload & insert it, it works fine, so you can also try to use the other browser.
If still not work, please post your WP login information with private reply, I will help you to fix it soon!
Thanks!