OK, so I found what I did wrong. I had the following in my functions.php file.
function order_events($query) {
global $wp_query;
if( $wp_query === $query && is_post_type_archive("event") ) {
$query->set( "event_start_before", "today" );
$query->set( "orderby", "eventstart" );
$query->set( "order", "DESC" );
}
}
add_action("pre_get_posts", "order_events", 1);
Needed to make this only apply to my theme, and not the admin, so I changed…
if( $wp_query === $query && is_post_type_archive("event") ) {
to…
if( !is_admin() && $wp_query === $query && is_post_type_archive("event") ) {
and that fixed everything.
Should have noticed that sooner. Thanks for the great plugin!