You’ll want to look at the redirects in your _redirects file and check that they have the ! if you want to force the redirect. The changes to redirects can be boiled down to:
If you have a redirect rule that’s not explicitly marked as forced, and you also have a file under the same path, we will serve the file.
and our CTO goes into much more detail in his post here:
The syntax for a forced redirect would be:
/new-home.html /old-home.html 301!
The syntax for an unforced redirect (that enables shadowing) would be:
/tshirts/* /other-summer-clothes.html 301
Let us know if we can answer any other questions about this!