IntelliJ shortcut to comment line
Solution 1:
References
https://www.jetbrains.com/help/idea/mastering-keyboard-shortcuts.html
Try to use Ctrl+Slash or Ctrl+Shift+Slash for block comment
If this doesn't work show in your Setting -> Keymap -> Search comment
Solution 2:
Use CTRL+/, but with the / located on the numpad.
The question remains why commenting with / (the one besides .) does not work (it does not for me, either).