I experience this problem as well - whenever I have selected a file within a PathFinder window. But I recently noticed that the feature works fine (click to select, then click again to edit filename) works fine for a file on the (PathFinder) desktop.
Thanks for the tip about using the keypad Enter key.
So guys, I'm just wondering, I see this thread gets closed and then re-opened, then closed, then re-opened. What is the status of this bug? It seems enough people are experiencing this that it has not been completely resolved. I've searched through numerous posts here and don't find a solution to the "slow double-click to rename", only work arounds. I just updated to version 8.3.8 (on Mac OS 10.13.6), and still cannot use the slow double-click to do a file rename, which is the normal Finder option (which does work, BTW). Would love to know if this is being worked on...or not.
Just responding to the latest post, although I had posted about this before Nov 15, 2018. I still cannot click-to-rename WHEN I am in COLUMNS view. However, I have found that when I am in ICON view or LIST view (as well as when I am on the desktop), I have no problem clicking-to-rename.
My default (and preferred) view is COLUMNS. So, when I want to rename a file, I quickly switch to LIST view, rename the file, and return to COLUMNS view. Clearly this is clunky, but it is not as frustrating as repeatedly trying to slowly double-click or change to Info panel to rename.