When I am running Git Bash, I occasionally accidentally press CTRL+I and this freezes up the terminal for quite a long time, before releasing.
I have tried CTRL+D, CTRL+Q, CTRL+C thereafter, but to no avail.
My only options at present are to simply wait or to forcefully close the Git Bash window. Neither of which are acceptable.
Does anyone know what CTRL+I is doing? And is there an easy way to cancel it after accidentally pressing it?
As wildplasser said in a comment, CTRL+I is the same as TAB. In bash, the tab key invokes the tab completion code, which searches around to see what words fit with whatever you have typed so far. On Unix-y systems this is generally pretty fast. Apparently it's horribly slow on your system. You might be able to speed it up, but if all else fails, you can just disable it.
See also git bash auto complete slow on windows 7 x64, https://blog.entelect.co.za/view/7554/speed-up-git-bash-on-windows, and https://superuser.com/questions/421397/disable-bashs-programmable-autocompletion-based-on-command.