CloudFront Custom 400 Error Page

Hi, I have set up a CloudFront infront of my ALB and have created a custom error page pointing to my S3 bucket. I can access the error page using the cloudfront URL with a /Errors_4xx/400.htm. However, when I trigger the actual 400 error (cloudfront URL with a /%20+%20%%% at the end), I get an error message '400 ERROR. The request could not be satisfied.'