vim CTRL-] keys not working

First, use the :verbose command (thanks to sehe) to know who rebound your key where.

:verbose nmap <C-]>

Then, if you cannot find where your key was rebound, bind yourCtrl-] key by the original one then retry:

:nnoremap <C-]> <C-]>

For more info:

:help mapping
:help :verbose
:help :noremap

I have the same issue, and :verbose did not bring up anything useful. What I figured out is that Ctrl-+ takes me there.

Please note that I am using a German keyboard where the plus sign sits at the position of square bracket on a US keyboard. Maybe the code only looks at the location of the key (I remember reading something to that respect in combination with the Ctrl-key).