Cannot open subsequent email attachments

Whenever I am sending an email from CRM which has more than one attachment, the receiver can only open one of the attachments.

Any subsequent attachments show the following error when trying to open:

This is only happening when sending emails from a contact or lead record within CRM.

We also use Zoho Mail Add On, and when sending an email from the Email tab, the attachments can be opened correctly.

Please can you advise?