Hello @t_schoftner,
Thanks for asking and please accept my apologies for the confusion. At times it becomes difficult to support 3rd party plugins and that’s the reason why as stated in our support policy, we don’t provide support for 3rd party plugins. But I can definitely point you in right direction. 
I wanted to know what’s the issue over here regarding Nextgen gallery. To test if there is any conflict with theme, I installed Nextgen gallery on my localhost and created few galleries and albums. In Order to increase the probability of conflict I set up Ethos stack to display gallery both using Cornerstone builder and WordPress WYSIWYG editor. But I am unable to replicate the problem on my end and it’s working absolutely fine. Please see screencast https://screencast.com/t/HRPjfa2Q, https://screencast.com/t/zb7MiZ3W
I also checked your website on chrome devtools and I don’t see any error messages up there. However, I see that upon clicking on the gallery thumbnail icons the URL is changing but content of galleries won’t open. So here are few things that I can suggest you as of now:
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Reset all options to default settings. Under Gallery > Other options > Click Reset Options and reset all options. This will not have any effect to the gallery.
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Check for plugin conflict by deactivating all the plugins including Nextgen gallery. After that reactivate Nextgen gallery and see if that fixes the problem. Next step would be reactivate one plugin at a time to narrow down the plugins that is causing the problem.
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Upon Googling it seems that the last version of Nextgen gallery 2.2.14 has few issues. If the above solutions didnt work out for you, then my suggestion would be downgrade the plugin to an earlier version and see if that resolves the issue for you.
Thanks.