Oh boy, you are in for a rough ride! I have been trying for two weeks to get High Sierra to work with my WD external drive. I started with WD tech support. Long story, but bottom line is nothing worked (I also tried the erase, restart, etc.).
Then turned to Apple tech support. After extensive work with 3 techs, they finally turned me over to a Senior Advisor. He has worked with me for most of a week to no avail. As of now, I have sent a ton of systems to him (that took 3 tries and 2 days!) so he can refer the problem to their engineers. Hope to hear back from them this coming Monday (12/18/17).
The problem is High Sierra. WD external drives seem to work with all previous Apple operating systems (although El Capitan was “quirky”).
If the Apple engineers actually solve my problem, I will post back to this Community. In the meantime, don’t waste too much time trying to solve your problem. Nothing seems to work until Apple fixes High Sierra.