Permissions Issue

I'll start by saying that, pre-El Capitan, I would have tried tackling this issue with the Repair Permissions action through Disk Utility. However, with that option gone (since it "just works" now, right?) I'm a bit flummoxed on how to rectify this issue.

Specs:
MacBook Pro (Retina, 15-inch, Mid 2014)
macOS Sierra Version 10.12.4
Capture One Pro 10.0.2

The Problem:
I have a large (4TB Lacie Rugged RAID) pocket drive that I use as my primary day-to-day editing drive. When trying to edit on images on the drive, I am now running into permissions errors that did not use to crop up.

ex: When trying to rename images I get an error "Could not rename image ___ to ___. The new name is already taken or you do not have write privileges. Please format name differently of check your access privileges.

(I have of course checked to confirm there are not in fact any naming conflicts.)

The permission issue is not restricted to renaming, this was just the easiest way for me to generate an error dialog. Much more frustratingly, any edits I make to the image settings are not saved upon relaunching the session, but resulting in no error dialog.

A Little History:
I recently had some issues with an older user account on this laptop. After a frustrating week of trying to diagnose and fix the issues, I ended up making a brand new user account and migrating items and setting up the new account manually. I suspect this is the root of these issues.

Troubleshooting:
Firstly I checked the finder permissions (Get Info > Sharing & Permissions > Unlock > Change all settings to Read & Write > Apply to enclosed Items)

I did this on the root directory of the external drive in question, and then each step of the way down to the individual raw files themselves.

I should note that originally the root directory was set to Read & Write for all, but the RAW files and containing folders were set to Read Only.

That said, I changed all the permissions in this way, even restarted and confirmed, but unfortunately the permissions issues within Capture One persist.

Next, I tried copying and moving (Separately) these files onto a local volume. As expected, the copy action resulted in resetting permissions and I was able to work with these files normally. The moved files were still uneditable within Capture One.

I also noted that even within Finder, if I tried to rename these files, I was prompted to enter an administrator password, which was not previously true. I also have run into an issue a few times where this drive would not unmount without fully shutting down and restarting the machine. There are no programs that I can see that would have been accessing the disk when this happened. Because of this I suspect the permissions error is with the Drive / Finder as opposed to Capture One, but I was hoping someone here might have experience with this and be able to suggest another fix.

If I had another 4TB Drive handy I could do a full copy, but I'm hoping there is a better option that would save me sourcing another volume that size and the time required to copy nearly 4TB of data twice.

Thanks in advance for any advice!