This sounds more like a problem with your phone, rather than Samsung Wallet. Something is interfering with the interface. If it were the actual app, everyone would have that problem. Clearing the cache is not ridiculous, it is basic phone maintenance. If it works after you clear the cache, then the problem is most definitely with your phone. If it doesn't work after that, there are other troubleshooting steps to take - probably none of which you'd like.
One solution would be to uninstall and reinstall the app, which would necessitate adding all your cards back. There was an update to the app this morning, maybe it helped? Which app are you using, the phone or the watch?
I'm using both apps, Samsung Wallet on the watch and Samsung wallet on my phone. When you click the plus icon to add a card on the watch it opens the phone app. When I choose a card to add to the watch I get a popup message saying "The card has already been added. The card information you entered has been discarded."
Have you tried import to see if there are cards available to import? Also the watch should not open the phone app, it should open the pay app through the wear app. Try going into the watch app from within the wear app rather than the watch. Watch settings/pay. Then when you hit the + sign, choose import. If it days no cards to import, try again to add. If it still says card has already been added. You will have to reset the app, ehich you can do from wirhin the Pay settings.
