Why did a lot of 404 errors pop up after installing a new layout?

Question

PHP

Hello!
after installing a new layout while maintaining the functionality, a lot of 404 errors popped up - about 2500 according to the Google and Yandex webmaster.
I look at these URLs - they really didn’t exist, and they look like this - as if some other non-existent address was attached to a regular article, for example.
What is the problem, why is it so, and how to fix it? what can it affect?

Answer 1

it looks like links to files (probably images) that were incorrectly spelled out in the layout.

Answer 2

It looks like an incorrect web.config setting, adding an extra slash - on the face - the rest - only after reviewing the code, options - I have 3