Photoshop wont recognize extra scratch disk space on external drive

I'm working on a 2017 Macbook pro and have had many issues with my scratch disk space in the past so I bought an external drive to store my apps and projects. At some point, most likely after I updated the app, the scratch disk setting switched back to my OS and I am now having the issues again. My main problem now is that when I try setting my external drive as the scratch disk again, photoshop doesn't recognize the available space on the drive and it reads as having the same amount of space as my OS. They both read as having about 7GB of extra space (criminally low I know lol) despite there being around 145GB of space available on the external, so I am still getting errors. When I've had this issue in the past I assumed that the low disk space was causing errors in its ability to read the external, but cleaning out my OS disk didn't help the problem. 

The external drive has already been reformatted as a MacOS extended (journaled) and has been working well for a while now. I am also working with the most recent version of Photoshop, however, I've had this issue with previous versions and at some point it corrects itself. I figured I'd ask this time though so I can prevent it from happening in the future and know how to fix it myself.