Computer slows down when I plug in a USB 3 flash drive

Do not know if this model is similar enough, but have seen other Gigabyte boards needing IOMMU in UEFI changes and the boot parameter iommu=soft

GIGABYTE GA-970A-DS3 motherboard not working with 64 bit kernel - IOMMU GRUB_CMDLINE_LINUX="iommu=soft"

https://ubuntuforums.org/showthread.php?t=2188370

Similar issues:

http://ubuntuforums.org/showthread.php?t=2111223&page=5

http://ubuntuforums.org/showthread.php?t=2292025

Does your USB flash drive have an activity LED? Is it flashing rapidly when you plug it in? If you do not have an activity LED, run

sudo apt-get install dstat

then run

dstat

Look at your CPU and Disk usage, and see what is using up your resources.

Also keep in mind that dstat will run until you tell it to stop, so remember to CTRL-Z when you're done.

Dstat can still be helpful even if you DO have an LED to look at because it will also display your CPU, Network, and other resources. Which may be helpful in solving your issue.