SOLUTION for scratch disk assignment resets to default on close

I can't believe I just stumbled into the solution for this years long issue! I've tested it multiple times and it works - your scratch disk assignment will stick and save.

Go to scratch disk settings

Double click on the disk you want to assign -  a check box will appear in the column labeled "Active?"

Click on the box to enable a checkmark - this will highlight that row

Use the arrows on the right to move the check marked disk up or down in priority

Do NOT uncheck the boxes after you assign order!

Click OK.

( I'm running Elements 2020 )

Close Photoshop Elements

Open Elements - confirm scratch disk assignments persisted after closing.