I've fixed the problem!
Drag the problem applications out of the Applications folder and into the Trash. (If you downloaded them from the Mac App Store you may have to authorize to do this.) Then drag them back to the Applications folder again.
Lauch Launchpad again. The icons might take moment to show up, but when they do, they should be the proper resolution icon.
If this doesn't help, I did also reboot before trying this action. So maybe you have to reboot first and do the above.
Cheers and let me know if this works for you.
P.S. the Apple Tech thought I was talking about pixelated icons in the dock and suggested removing and then adding them back to the Dock, but this was for Launchpad. So I tried doing the same by removing and adding it back to the Applications folder via the Trash. Seems to have worked and got to teach the Apple Rep a trick too. 🙂