Firstly, in contradiction to answer by Reza, this could be an error which needs some additional steps to fix it.
Why 404 error appears?
It appears if you deleted a page, replaced a page (your scenario falls in it), or the page doesn't exist but discoverable (typo errors in anchor links, backlinks, query filter links which may not exist anymore or appear again later).
Covering your case of replacement, you need to do the following:
- Remove the discovery of old links
- Update your internal links (navigations, within post/page contents) by removing last hash from them.
- Do the same for backlinks (obviously which you have access to)
- Redirect all pages with ending hash to without hash via .htaccess or it is better to use redirection tool (if you are on WP) - add permanent 301 redirect. This will help Google to understand, the page is replaced.
- Go to Google search console > Indexing > Pages > Not found (404) > mark validate fix and wait for the Google to crawl those pages again, find them redirected (fixed), and update you back.
If you don't remove discovery sources, this will keep coming again. However, Google do not prefer to crawl repeatedly on the pages with errors. So, you would see them coming again but less often.
Reference: Guide to fix search console 404 errors.
Disclosure: this is published by me for my community, students, and clients.