In your AWS Console > Amplify, select your app, select Hosting > Rewrites and redirects. If there is a redirect for <*> to /index.html with type 400, that is the issue.

For non-SPAs change the type to 200.

For SPAs, can remove the 404 rewrite, and it is recommended to use:

Source: </^[^.]+$|.(?!(css|gif|ico|jpg|js|png|txt|svg|woff|woff2|ttf|map|json|webp)$)([^.]+$)/>

Target: /index.html

Type: 200 (Rewrite)

Source: https://docs.aws.amazon.com/amplify/latest/userguide/redirect-rewrite-examples.html