upgrade wp5 generates page 404

Hello, following my update to WP 5 I also have a problem with a generation of pages 404 that are listed on my activity dashboard.
Example of all the pages 404 message error I have:
France left https://heulys.com/wp-content/themes/u-design/assets/css/frontend/global/custom_style.css?ver=3.0.0.… and tried to access non-existent page https://heulys.com/wp-content/themes/u-design/assets/css/frontend/common-images/home-page-content-top.png

Manchester, United Kingdom left https://heulys.com/4-ways-to-admire-pittsburgh-skyline/ and tried to access non-existent page https://heulys.com/wp-content/themes/u-design/assets/css/frontend/common-images/home-page-content-top.png
etc….
On the other hand, this is transparent for the reader who has access to the post. he actually sees the correct page (of a post) and not a page 404.

And at the same time, my security plugin (Wordfence Security) has sent me a message telling me that 151 files are not recognized. “These files are in a WordPress core location but is not distributed with this version of WordPress. This is usually due to it being left over from a previous WordPress update, but it may also have been added by another plugin or a malicious file added by an attacker.” Should I delete them ? This problem is it related to the pages 404 I mentionned above ?
The page I need help is https://heulys.com/

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