You would like download more than one file from Attachments at the same time in your system, but it is not working for you to select multiple files.
SAP Hybris Cloud for Customer;
It is not possible to download multiple files directly from attachments tab, but since the 1802 release you can do this action by Library workcenter.
Go to Library workcenter and select Attachments.
You can also to use the Advanced Search to filter the attachments files by Object (Account, Opportunity, Visit, etc).
Download; Multiple; Attachments; Files; More; One; , KBA , AP-RC-MOB-UIF , Responsive UI , How To
SAP Cloud for Customer add-ins all versions ; SAP Cloud for Customer core applications all versions