Error 500 – Internal server error

Hello Team,
after activating your plugin Ocean Extra I get an error message in the backend (the frontend still works):

Error 500 – Internal server error

Could you please tell me how can I solve this problem.

This is the info from Elementor information:

—————————————————————-
== Server Environment ==
Operating System: Linux
Software: Apache
MySQL version: MySQL Community Server (GPL) v5.7.30
PHP Version: 7.4.5
PHP Max Input Vars: 5000
PHP Max Post Size: 64M
GD Installed: Yes
ZIP Installed: Yes
Write Permissions: All right
Elementor Library: Connected

== WordPress Environment ==
Version: 5.4.1
Site URL: https://www.XXXXX
Home URL: https://www.XXXXX
WP Multisite: No
Max Upload Size: 64 MB
Memory limit: 512M
Permalink Structure: /%postname%/
Language: de-DE
Timezone: Europe/Berlin
Debug Mode: Inactive

== Theme ==
Name: OceanWP
Version: 1.8.3
Author: Nick
Child Theme: No

== User ==
Role: administrator
WP Profile lang: de_DE
User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/83.0.4103.61 Safari/537.36

== Active Plugins ==
Elementor
Version: 2.9.11
Author: Elementor.com

Fluent Forms – Best Form Plugin for WordPress
Version: 3.5.6
Author: WP Fluent Forms

NinjaFirewall (WP Edition)
Version: 4.2.1
Author: The Ninja Technologies Network

Ocean Custom Sidebar
Version: 1.0.6
Author: OceanWP

Ocean Modal Window
Version: 1.1.0
Author: OceanWP

Simple Side Tab
Version: 1.2.1
Author: Scot Rumery

== Must-Use Plugins ==
0-ninjafirewall.php
Version: 1.0
Author: The Ninja Technologies Network

== Elements Usage ==

wp-page : 5
button : 1
heading : 1
icon-box : 3
text-editor : 4

== Log ==

PHP: showing 1 of 1PHP: 2020-05-22 13:18:54 [notice X 2][/homepages/7/d183421784/htdocs/XXXXX/wp-content/plugins/elementor/includes/api.php::160] Undefined index: pro_widgets [array (
‘trace’ => ‘
#0: Elementor\Core\Logger\Manager -> shutdown()
‘,
)]

Log: showing 1 of 12020-06-02 20:23:43 [info] Elementor data updater process has been completed. [array (
‘plugin’ => ‘Elementor’,
‘from’ => ‘2.9.8’,
‘to’ => ‘2.9.11’,
)]

—————————————————————–

Thanks.
Alex