Sometimes attachment stops working. This techdoc explains one use case why it stops working.
Release : 17.2
Component : SDM - Attachments
The Service Desk install folder\bopcfg\www\CATALINA_BASE\temp is used as a transition folder before the attachments and exports get to their final location. However, due to some operation reason like end users cancel the export when it is half done, files will stuck in here. If more and more files fill out this temp folder, attachment operation will take long time and this long time sometimes cause the end user attachment failure. The recommendation is this temp folder should be emptied from time to time either manually or by some auto script that scheduled to run when no users are online or when Service Desk restarts.