There's a bug in macOS where if you're using a different keyboard layout (I use DVORAK) any keyboard overrides that you configure for your mouse buttons look like they get captured correctly. But when triggered they revert to the QWERTY layout for those key presses. In my case I tried to map cmd+[ to the back button for an app. But this triggers cmd+ + (which is where that key is on a QWERTY keyboard).