Can’t add new Location

I need a bit more info here … is there anything in the browser console? Anything in the server logfiles? What is happening when you press submit? Is your windows blocking you in some way?
Without more info, nothing I can tell here …

The Chrome console shows:
JQMIGRATE: Migrate is installed, version 1.4.1
admin.php?page=eme-locations:1 The SSL certificate used to load resources from https://www.paypal.com will be distrusted in M70. Once distrusted, users will be prevented from loading these resources. See https://g.co/chrome/symantecpkicerts for more information.
plugin.min.js?ver=4607-20171116:1 Deprecated TinyMCE API call: <target>.onNodeChange.add(..)

No related errors in the server log.

In Windows 10 and Chrome, the background turns blue while I hold down the mouse button, but nothing happens.

The “Add location” screen looks odd, as if the application form is superimposed over a blank WordPress screen.

I also tested it on my MacBook Pro (OS X 10.1.6) on Chrome and Firefox with the same results.

Since you also have some paypal plugin installed, I’d advise to disable all other plugins and try again. Something is blocking you for sure …

The conflict is apparently with RSVPMaker plug-in. Problem goes away if I deactivate RSVPMaker.
How might I go about resolving this conflict?

You need to check with them: they include their CSS and javascript files on all admin pages (tested here), causing issues to other plugins (next to the fact that the plugin is not tested with the current wordpress version and has php warnings upon activation). Their function rsvpmaker_admin_enqueue() is not completely implemented.