Whenever you upload a file to S3, you are creating a URL. To ensure that you are safe, you may want to evaluate the file names that you are using.
I recommend the following regular expression (RegEx)
Any file name that doesn't match that pattern you may want to change in an effort to be URL compliant.
AWS is CasE-SensITive primarily because it is meant as an Object Store. When persisting objects. Many times objects that are written are persisted with a base64 URL Safe encoded hash in order to create a more reliable search time for objects during retrieval.