Quiz editor broken?

WordPress
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Version: 4.9.5
Debug Mode: Yes
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Show On Front: posts
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Settings
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Version: 3.17.4
Db Version: 3.17.4
Course Catalog: Katalog kursów (#1379)
Course Catalog Per Page: 9
Course Catalog Sorting: menu_order
Membership Catalog: Katalog cz?onkostw (#1380)
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Checkout Address: required
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Cert Bg Width: 800
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Server
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Mysql Version: 5.7.16
Php Curl: Yes
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Browser
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HTTP USER AGENT: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_13_4) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/66.0.3359.117 Safari/537.36

Theme
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Version: 1.0.0
Template: verbosa
Child Theme: Yes
Llms Support: No

Plugins
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LifterLMS: 3.17.4

Integrations
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BbPress: No
BuddyPress: No

Template Overrides
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When I try to add a new question to the quiz (click on Add Question) there’s an error in the console:

editor.min.js?ver=4.9.5:1 Uncaught TypeError: Cannot read property 'translate' of undefined
    at Object.b.editor.initialize (editor.min.js?ver=4.9.5:1)
    at n.init_editor (_Editable.js:517)
    at n.render (QuizHeader.js:57)
    at n.render_subview (_Subview.js:166)
    at n.render (Quiz.js:138)
    at n.render_subview (_Subview.js:166)
    at n.<anonymous> (_Subview.js:132)
    at underscore.min.js?ver=1.8.3:5
    at Function.m.each.m.forEach (underscore.min.js?ver=1.8.3:5)
    at n.render_subviews (_Subview.js:128)

Moreover, when I click on “Add Existing Lesson”, the server responds with an error:

Deprecated: Non-static method LLMS_Admin_Builder::get_existing_posts_where() should not be called statically in /usr/home/…/public_html/wp-includes/class-wp-hook.php on line 286

I don’t have any plugins enabled.