Open folder /home/USERNAME/.local/share/applications/

Find jetbrains-idea.desktop.

Right mouse click on it, then select Properties

Open Application tab

Next to the Command section click Browse… button and select idea.sh file in /pathToIntelliJ/bin folder. (In my case the path was already correct, but it seems that selection the file again rewrite something and Icon works ok now).

Click OK.

https://stackoverflow.com/questions/43706663/intellij-idea-lost-icon-after-launch