While running tests on SiteGround I ran into a situation where their high security measures were blocking the NextGEN Gallery Export Lightroom plugin from performing its tasks.
In fact, at some point SiteGround thought that the plugin was doing an attack on the server. That's not SiteGround's fault. In fact, I'm glad it caught it because I don't want my site's being attacked.
But the issue that came up was that I was then blocked from my own website. I couldn't access the backend or view the front end.
What to do
If you find yourself in this situation, contact your host and ask them to check their firewall and modsecurity settings. Give them your IP to unblock (Google What's My IP on Google?) and then remove the mod security rule that is blocking the Lightroom uploads.
For example, the following was added to the htaccess file on the site in question, and from there on I was no longer blocked from uploading from Lightroom to NextGEN Gallery.
<IfModule mod_security.c> SecFilterRemove 001285 </IfModule>
Our developers believe that's a custom rule that SiteGround created to protect their customers. So the modsecurity rule may not work on your site.
We've seen great successes with both SiteGround and WP Engine with handling bulk uploads from Lightroom to NextGEN Gallery. But there is no reason any host shouldn't be able to handle it.
I also recommend enabling the throttle feature in the Lightroom plugin, if you find yourself constantly being blocked. Each host and server is different. Each has their own security measures, and can handle its own bandwidth.
So do some troubleshooting with your host's customer service department if needed.