iTerm2 closing curly brace not working

I had the same issue using iTerm2 3.1.6 and a German keyboard layout.

In my case, it was caused by the option To switch split planes: being set to ⌥ Number). This option can be found in Preferences > Keys > Navigation Shortcuts.

Any other setting for this option works as a workaround for the issue.

For me it turns out the right ALT key works but not the left and it's because the left ALT key had a different setting.

You can change this by going to Preferences -> Profiles -> Keys and changing from Esc+ to Normal