I updated to High Sierra on my Macbook Pro when it was released. Since I have updated, a lot of my applications show the attached icon when I open them. Does anyone know a fix to this?
Rebooting in "Safe Mode" fixes this issue. Probably because system caches are cleared and re-created during safe boot.
To boot in Safe Mode, hold the shift key while starting or rebooting the Mac. You can release the shift key when the login prompt appears.
Apple provides more details about Safe Mode in this article.
Do you have the game "League of Legends" installed on your Mac ?
Other persons having this problem have reported that the update process of League of Legend may cause this issue.
If so, please upvote this issue on the LoL forum, to report it to developers : https://boards.na.leagueoflegends.com/en/c/bug-report/rA0p1rYx-client-updating-on-mac-high-sierra-messes-up-other-application-icons