When testing the LG G5 with the Samsung Portable SSD T3 and I had been fooled into thinking that the LG G5 supported only USB 2.0 speeds. Turns out that this is only true when the LG G5 is a USB Host.
In fact, when connecting the LG G5 to a USB 3.1 Gen 1 port on a Mac, you can see that the LG G5 actually enumerates as a USB 3.1 Gen 1 peripheral. This can be confusing that the same USB port, depending on whether the LG G5 is the host or peripheral, enumerates at a different speed.
To take advantage of the faster USB 3.1 Gen 1 speeds, I was excited to try out Android File Transfer to transfer photos and videos from the LG G5 to the Mac. Unfortunately, Android File Transfer was unable to copy any files from the LG G5 to the Mac even though I had selected the MTP option for the USB connection on the phone.
Every time I tried to copy a file, I got a "Could not copy the file ..." error.
Even after deleting the Android File Transfer Application, and downloading and installing it again from Google, I still was unable to transfer any files.
To get around this, I had to switch to PTP mode for the LG G5 USB connection.
This allowed me to then use Image Capture Application on the Mac to download the video and photos. Note using PTP doesn't allow you to copy files from the Mac to the LG G5.