I also failed to make Vim plugin work. From CodeMirror official site
Note: The CodeMirror vim bindings do not have an active maintainer. That means that if you report bugs in it, they are likely to go unanswered. It also means that if you want to help, you are very welcome to look at the open issues and see which ones you can solve.
But still, it could be an error in TiddlyWiki. Nonetheless, for the time being, I have switched to Wasavi addon on to get Vim inside TiddlyWiki editor.
I just added to my TW (5.1.17) wiki the main CM plugin along with the vim keymap plugin for it. It's not working.index.html:11067 Error executing boot module $:/plugins/tiddlywiki/codemirror/keymap/vim.js: "Cannot find module named '../addon/edit/matchbrackets.js' required by module '$:/plugins/tiddlywiki/codemirror/keymap/vim.js', resolved to $:/plugins/tiddlywiki/codemirror/addon/edit/matchbrackets.js"
I gave a try to codemirror and its Vim keymap again. It turned out then I need all following plugins to make codemirror work with Vim keymaps
"tiddlywiki/codemirror",
"tiddlywiki/codemirror-closebrackets",
"tiddlywiki/codemirror-keymap-vim",
"tiddlywiki/codemirror-search-replace",
Hope someone else will find it useful.