Error on clicking 'Screen Options' tab only at Products-related editor screen(s) and for specific user

My client has problems with the Screen Options tab and in general with Javascript (or maybe WPBakery) related parts of the Admin screen.

WPBakery-s blue buttons are not displaying to him at all. And it happens only, if he stays on a Product Editor page or on other screen that is Product-related.

MY client's screenshot:

My screenshot, at same product

For me everything works flawlessly.

We tired the following:

1. with different user (admin)
2. from other browser

DevTools Console gives the following error:

wp-auth-check.min.js?ver=5.4.2:2 Uncaught TypeError: Cannot read property 'hasClass' of undefined
    at HTMLDocument.anonymous (wp-auth-check.min.js?ver=5.4.2:2)
    at HTMLDocument.dispatch (load-scripts.php?c=1load[chunk_0]=jquery-core,jquery-migrate,utils,jquery-ui-core,jquery-ui-widget,jquery-ui-mouse,jquery-ui-sliderver=5.4.2:3)
    at HTMLDocument.r.handle (load-scripts.php?c=1load[chunk_0]=jquery-core,jquery-migrate,utils,jquery-ui-core,jquery-ui-widget,jquery-ui-mouse,jquery-ui-sliderver=5.4.2:3)
    at Object.trigger (load-scripts.php?c=1load[chunk_0]=jquery-core,jquery-migrate,utils,jquery-ui-core,jquery-ui-widget,jquery-ui-mouse,jquery-ui-sliderver=5.4.2:3)
    at Object.a.event.trigger (load-scripts.php?c=1load[chunk_0]=jquery-core,jquery-migrate,utils,jquery-ui-core,jquery-ui-widget,jquery-ui-mouse,jquery-ui-sliderver=5.4.2:8)
    at HTMLDocument.anonymous (load-scripts.php?c=1load[chunk_0]=jquery-core,jquery-migrate,utils,jquery-ui-core,jquery-ui-widget,jquery-ui-mouse,jquery-ui-sliderver=5.4.2:3)
    at Function.each (load-scripts.php?c=1load[chunk_0]=jquery-core,jquery-migrate,utils,jquery-ui-core,jquery-ui-widget,jquery-ui-mouse,jquery-ui-sliderver=5.4.2:2)
    at a.fn.init.each (load-scripts.php?c=1load[chunk_0]=jquery-core,jquery-migrate,utils,jquery-ui-core,jquery-ui-widget,jquery-ui-mouse,jquery-ui-sliderver=5.4.2:2)
    at a.fn.init.trigger (load-scripts.php?c=1load[chunk_0]=jquery-core,jquery-migrate,utils,jquery-ui-core,jquery-ui-widget,jquery-ui-mouse,jquery-ui-sliderver=5.4.2:3)
    at Object.anonymous (load-scripts.php?c=1load[chunk_0]=hoverIntent,common,hoverintent-js,admin-bar,heartbeat,autosave,wp-ajax-response,jquery-color,wp-lists,quicktags,jquery-query,admload[chunk_1]=in-comments,suggest,postbox,jquery-ui-position,jquery-ui-menu,jquery-ui-autocomplete,tags-suggest,tags-box,word-count,wp-sanitizload[chunk_2]=e,post,editor-expand,thickbox,shortcode,wp-pluploadver=5.4.2:11)
(anonymous) @ wp-auth-check.min.js?ver=5.4.2:2
dispatch @ load-scripts.php?c=1load[chunk_0]=jquery-core,jquery-migrate,utils,jquery-ui-core,jquery-ui-widget,jquery-ui-mouse,jquery-ui-sliderver=5.4.2:3
r.handle @ load-scripts.php?c=1load[chunk_0]=jquery-core,jquery-migrate,utils,jquery-ui-core,jquery-ui-widget,jquery-ui-mouse,jquery-ui-sliderver=5.4.2:3
trigger @ load-scripts.php?c=1load[chunk_0]=jquery-core,jquery-migrate,utils,jquery-ui-core,jquery-ui-widget,jquery-ui-mouse,jquery-ui-sliderver=5.4.2:3
a.event.trigger @ load-scripts.php?c=1load[chunk_0]=jquery-core,jquery-migrate,utils,jquery-ui-core,jquery-ui-widget,jquery-ui-mouse,jquery-ui-sliderver=5.4.2:8
(anonymous) @ load-scripts.php?c=1load[chunk_0]=jquery-core,jquery-migrate,utils,jquery-ui-core,jquery-ui-widget,jquery-ui-mouse,jquery-ui-sliderver=5.4.2:3
each @ load-scripts.php?c=1load[chunk_0]=jquery-core,jquery-migrate,utils,jquery-ui-core,jquery-ui-widget,jquery-ui-mouse,jquery-ui-sliderver=5.4.2:2
each @ load-scripts.php?c=1load[chunk_0]=jquery-core,jquery-migrate,utils,jquery-ui-core,jquery-ui-widget,jquery-ui-mouse,jquery-ui-sliderver=5.4.2:2
trigger @ load-scripts.php?c=1load[chunk_0]=jquery-core,jquery-migrate,utils,jquery-ui-core,jquery-ui-widget,jquery-ui-mouse,jquery-ui-sliderver=5.4.2:3
(anonymous) @ load-scripts.php?c=1load[chunk_0]=hoverIntent,common,hoverintent-js,admin-bar,heartbeat,autosave,wp-ajax-response,jquery-color,wp-lists,quicktags,jquery-query,admload[chunk_1]=in-comments,suggest,postbox,jquery-ui-position,jquery-ui-menu,jquery-ui-autocomplete,tags-suggest,tags-box,word-count,wp-sanitizload[chunk_2]=e,post,editor-expand,thickbox,shortcode,wp-pluploadver=5.4.2:11
i @ load-scripts.php?c=1load[chunk_0]=jquery-core,jquery-migrate,utils,jquery-ui-core,jquery-ui-widget,jquery-ui-mouse,jquery-ui-sliderver=5.4.2:2
fireWith @ load-scripts.php?c=1load[chunk_0]=jquery-core,jquery-migrate,utils,jquery-ui-core,jquery-ui-widget,jquery-ui-mouse,jquery-ui-sliderver=5.4.2:2
x @ load-scripts.php?c=1load[chunk_0]=jquery-core,jquery-migrate,utils,jquery-ui-core,jquery-ui-widget,jquery-ui-mouse,jquery-ui-sliderver=5.4.2:4
c @ load-scripts.php?c=1load[chunk_0]=jquery-core,jquery-migrate,utils,jquery-ui-core,jquery-ui-widget,jquery-ui-mouse,jquery-ui-sliderver=5.4.2:4
XMLHttpRequest.send (async)
send @ load-scripts.php?c=1load[chunk_0]=jquery-core,jquery-migrate,utils,jquery-ui-core,jquery-ui-widget,jquery-ui-mouse,jquery-ui-sliderver=5.4.2:4
ajax @ load-scripts.php?c=1load[chunk_0]=jquery-core,jquery-migrate,utils,jquery-ui-core,jquery-ui-widget,jquery-ui-mouse,jquery-ui-sliderver=5.4.2:4
l @ load-scripts.php?c=1load[chunk_0]=hoverIntent,common,hoverintent-js,admin-bar,heartbeat,autosave,wp-ajax-response,jquery-color,wp-lists,quicktags,jquery-query,admload[chunk_1]=in-comments,suggest,postbox,jquery-ui-position,jquery-ui-menu,jquery-ui-autocomplete,tags-suggest,tags-box,word-count,wp-sanitizload[chunk_2]=e,post,editor-expand,thickbox,shortcode,wp-pluploadver=5.4.2:11
(anonymous) @ load-scripts.php?c=1load[chunk_0]=hoverIntent,common,hoverintent-js,admin-bar,heartbeat,autosave,wp-ajax-response,jquery-color,wp-lists,quicktags,jquery-query,admload[chunk_1]=in-comments,suggest,postbox,jquery-ui-position,jquery-ui-menu,jquery-ui-autocomplete,tags-suggest,tags-box,word-count,wp-sanitizload[chunk_2]=e,post,editor-expand,thickbox,shortcode,wp-pluploadver=5.4.2:11
setTimeout (async)
d @ load-scripts.php?c=1load[chunk_0]=hoverIntent,common,hoverintent-js,admin-bar,heartbeat,autosave,wp-ajax-response,jquery-color,wp-lists,quicktags,jquery-query,admload[chunk_1]=in-comments,suggest,postbox,jquery-ui-position,jquery-ui-menu,jquery-ui-autocomplete,tags-suggest,tags-box,word-count,wp-sanitizload[chunk_2]=e,post,editor-expand,thickbox,shortcode,wp-pluploadver=5.4.2:11
v @ load-scripts.php?c=1load[chunk_0]=hoverIntent,common,hoverintent-js,admin-bar,heartbeat,autosave,wp-ajax-response,jquery-color,wp-lists,quicktags,jquery-query,admload[chunk_1]=in-comments,suggest,postbox,jquery-ui-position,jquery-ui-menu,jquery-ui-autocomplete,tags-suggest,tags-box,word-count,wp-sanitizload[chunk_2]=e,post,editor-expand,thickbox,shortcode,wp-pluploadver=5.4.2:11
h @ load-scripts.php?c=1load[chunk_0]=hoverIntent,common,hoverintent-js,admin-bar,heartbeat,autosave,wp-ajax-response,jquery-color,wp-lists,quicktags,jquery-query,admload[chunk_1]=in-comments,suggest,postbox,jquery-ui-position,jquery-ui-menu,jquery-ui-autocomplete,tags-suggest,tags-box,word-count,wp-sanitizload[chunk_2]=e,post,editor-expand,thickbox,shortcode,wp-pluploadver=5.4.2:11
(anonymous) @ load-scripts.php?c=1load[chunk_0]=hoverIntent,common,hoverintent-js,admin-bar,heartbeat,autosave,wp-ajax-response,jquery-color,wp-lists,quicktags,jquery-query,admload[chunk_1]=in-comments,suggest,postbox,jquery-ui-position,jquery-ui-menu,jquery-ui-autocomplete,tags-suggest,tags-box,word-count,wp-sanitizload[chunk_2]=e,post,editor-expand,thickbox,shortcode,wp-pluploadver=5.4.2:11
dispatch @ load-scripts.php?c=1load[chunk_0]=jquery-core,jquery-migrate,utils,jquery-ui-core,jquery-ui-widget,jquery-ui-mouse,jquery-ui-sliderver=5.4.2:3
r.handle @ load-scripts.php?c=1load[chunk_0]=jquery-core,jquery-migrate,utils,jquery-ui-core,jquery-ui-widget,jquery-ui-mouse,jquery-ui-sliderver=5.4.2:3

and i repeat: it's happening only for a specific computer, and seems to be not a user- or browser-level issue. (can it be IP related anyhow?!)

Thank you for any ideas.. Wiktor