I have a 1TB backup plus drive (Seagate) formatted using ExFAT, to be able to use it on Mac OS. I'm using an Early 2015 Macbook Pro Retina (13"), running OS X El Capitan 10.11.6.
From when I first started using the hard drive, it works perfectly fine once it's mounted. When it has been ejected improperly (yes, I know, I shouldn't, but it happens by accident sometimes) it will take ages (+- 20min) after plugging it in again for it to mount (show up in Finder). I tried opening Disk Utility to check if it shows up there, it never does. The delay is always there. Disk Utility just shows a spinner and doesn't even load my main HDD, unless I plug out the external HDD.
Also tried various commands in the Terminal, e.g.
diskutil mountDisk disk name and
diskutil mount volumeName, etc. Nothing seems to help, the delay is consistently there.
After reboot, it always shows up immediately, which tells me it's not the disk's fault.
Anyone have a solution to this? USB service restart or something like that?