Not able to mount EFI partition with diskutil after installing Ubuntu
Occasionally, you will encounter scarecrows. Here is one such example.

Observe:

Marlin:~ davidanderson$ diskutil mount disk0s1
Volume on disk0s1 failed to mount
If the volume is damaged, try the "readOnly" option
Marlin:~ davidanderson$ sudo diskutil mount disk0s1
Password:
Volume EFI on disk0s1 mounted
Marlin:~ davidanderson$


The message is meant to scare you, thus the term scarecrow. Nothing is wrong, you just need to add sudo.