For each website, domain.com/"anything that doesn't exist on the website" returns a 404 error. So why Google just reports some random URLs as 404?
Because There's/there have been a link somewhere pointing to it.
You need to check the "linked from" tab where the 404s are reported.
- Click on each error entry.
- Navigate to "linked from" tab.
- Check the web pages that are listed there and look for the URL of the 404 page inside the source of the page.
If you find the URL inside the source of the page, then the page will be crawled. You need to redirect address of the missing page to the new URL of it.
If you can't find the URL inside the source of the page, then it might be a temporary problem inside your website. In this case, simply mark the error as fixed.
If the errors that you mark as fix appear again, you need to check the new list of "linked from" pages and it means that there's still a link pointing to the page.
You can check the "date detected" and compare it with the date that you mark the error as fixed.
Please note that you need to be patient for this process since Google search console data belongs to a few days ago.
So for up to a week, mark all the errors as fixed and then wait for Google bot to show you the real missing pages.