The screen capture image indicates the Seagate USB external hard drive has two partitions, the first partition being a 128MB one with a unsupported file system, and a second main partition that is NTFS formatted. Could be your Synology was incorrectly reading the hard drive due to Partition 1 being there with an unsupported partition format. Then by adding the exFAT Access package it perhaps properly can deal with having the first partition being in an unsupported partition format.