External hard drives not unmounting-MAC OS MOJAVE- BRAND NEW MACS

Hi

I just upgraded all of my computers. They are all brand new iMacs (retina 5k 2017) or MacBook Pro (2018 Thunderbolt 3) laptops bought within the last 5 months. (Written on 04/2019) We have 2 laptops, and 5 iMacs.- and all of them are having issues in unmounting external hard drives. What is going on? The hard drives and thumb drives are from multiple clients around the world- so it isn't one style hard drive. Disk Utility is just keeps "loading disks" and never actually loads. A restart is necessary to get everything back on track. Anyone else having this issue?

Christina