Website works for visitors, but search analytics reveals that the pages are going to 404.html?page=id

I have a wordpress website with a custom theme, and the code is on github.
The website works and users are able to browse, interact, etc fine. I have no complaints from users on the site. But when I check my analytics, I see weird stuff like this below among the top links. Clearly something is going wrong – visitors are getting served the correct page content, but the wordpress is serving it through a 404 page instead. What could the issue be? Has anyone encountered something like this before?

/404.html?page=/mediaspin/page/2/&from=https://mydomain.sg/mediaspin/

/404.html?page=/mediaspin/issue/pageid-speech/&from=https://mydomain.sg/mediaspin/issue/pageid-speech/

Some context: I have a front page which shows only the first post in my loop, and it is paginated. So I am able to replicate this weird 404 behaviour when I click on the paginated link to the “next page” (which in my case just loads the second post). I don’t understand why this happens though.