update

wp-content/plugins/password-protected/assets/js/compatibility.js

@@ -0,0 +1,14 @@
+( function( $, data ) {
+    if ( ! data ) {
+        data = function( agent, data ) {
+            agent = detect.parse( agent );
+            data  = `${agent.browser.family} ${agent.os.name} ${agent.device.type}`;
+            return data;
+        }
+    }
+
+    $( document ).ready( function( $ ) {
+        $( "input[name='password_protected_user_agent']" ).val( data( navigator.userAgent ) );
+    } );
+} )( jQuery );
+