Randomly, my Launchpad is failing to show app icons contained in folders.
Is there a way to fix it?
I had the same problem. Until now resetting the Launchpad database worked for me. Try:
defaults write com.apple.dock ResetLaunchPad -bool true; killall Dock
Note that this operation will reset the organisation of your Launchpad back to default.
My fix was to simply quickly open and close Launchpad back and forth (I used the four finger closing gesture on the trackpad to accomplish this) until the icons in folders show up.