Hi There.
Just an update on my situation:
Had exactly the same issue as you, that's how I found your thread.
So, my issue was a dumb one, and if you lucky so is yours.
After hours of testing and checking and continuous Access Denied messages and concerned work mates. I remembered that I created a group policy for no USB or external storage device access... Oops... Seems that policy blocked way more that it should have.
Turns out, that was my problem. 🤦♂️
Exactly the same symptoms as what you are reporting here... Removing that policy sorted my issues out. Got full access to my drives now.