This could be due to many reasons and it is difficult to provide a proper answer without having more details. I would recommend following the below procedure.
a. First ensure the S3 bucket is properly configured to host a static site. This is a long shot but can start there. b. But my guess is it could be related to Route 53. I realised that you are using an A record but since there is an internal resource I think you will have to use an alias record. Refer below.
404 - Not Found error on static websiteasked 2 years ago
S3 static website domain not workingasked 24 days ago
Registered domain with AWS, configured Route 53 and S3. URL taking me to wrong website.asked 6 months ago
why www. prefix is required(must) with my domain hosted on AWS S3?Accepted Answerasked 3 years ago
Static Website S3 not resolving - DNS Provider is not AWSasked a year ago
Route 53 record test responds with DNS response code Non-Existent Domainasked 3 months ago
S3 Static Website RoutingRules when using Cloudfront and a domain nameasked 3 years ago
Static website in S3 not working with HTTPSasked 2 years ago
Deploying a static website on S3 but using domain name from 123Regasked 2 months ago
DNS_PROBE_FINISHED_NXDOMAIN with S3 static websiteAccepted Answerasked a year ago