Users are to transmit attachments via Connect Support. Chat agents might be able to add attachments but the end user will not be able to access the same.
All available releases
Failing Read ACL on sys_attachment table could be the reason
There is an out of the box ACL on sys_attachment table which allows end users read access to the attachments which they are entitled to see.
Users need to make sure this ACL is same as the out of the box one. If not, importing the OOB ACL to the instance will resolve the issue. They may also need to evaluate other read ACLs(if any) on the sys_attachment table to verify the user has enough permissions to view the records.