So you just have to redo all your settings in Wacom every time? That sucks.
It is a Wacom "issue" not Photoshop. Wacom stores the preferences by application and sees each version of Photoshop as a separate application. Rightly so as many of us have several versions of Photoshop installed.
You could use a text editor to directly edit the Wacom_Tablet.dat file (make a backup copy first first) but it may be quicker just to set up the preferences again.
1) If you had saved your Wacom préférences (using Wacom desktop center) restore them.
2) Run Photoshop 2018. Run the Wacom tablet Properties. Click to + to add Photoshop 2018 by searching the file on your computer (don't click to the name Photoshop that appear in the list) . Don't delete the old icons in the Wacom properties, they must absolutly stay. The properties you had for previous versions should appear for the new one (else set them up again, you should see them by clicking on an older version icon)
3) Save your préférences (using the Wacom Desktop Center)
Good luck !