A few months ago I noticed undo-tree was not working properly for me, though it had never been a problem in the past. Whenever I opened an existing file on my computer and edited it, trying to undo would give me a message saying "Undo-tree mode not enabled in buffer." If I manually enabled undo-tree mode per buffer everything would work fine, however that had never been the case before. It simply worked with my config.
Strangely it seems to be a key binding causing the problem. I'm using general.el to do my keybinds. Here is a minimal config that reproduces the issue:
(require 'package)
(add-to-list 'package-archives '("melpa" . "https://melpa.org/packages/") t)
(package-initialize)
(unless package-archive-contents
(package-refresh-contents))
(unless (package-installed-p 'use-package)
(package-install 'use-package))
(require 'use-package)
(setq use-package-always-ensure t)
(use-package evil
:init
(setq evil-want-integration t)
(setq evil-want-keybinding nil)
(setq evil-want-C-u-scroll t)
(setq evil-want-C-i-jump nil)
(setq evil-ex-search-vim-style-regexp t)
(setq evil-respect-visual-line-mode t)
; (defvar my/cur-window nil)
:config
(evil-mode 1)
(setq evil-vsplit-window-right t)
(setq evil-split-window-below t)
(setq evil-want-fine-undo t))
(use-package evil-collection
:after evil
:config
(evil-collection-init))
(use-package general
:ensure t
:config (general-evil-setup t))
(use-package undo-tree
:ensure t
:config
(evil-set-undo-system 'undo-tree)
(global-undo-tree-mode 1))
(nvmap :keymaps 'override
"/" 'swiper
"C-/" 'counsel-rg)
If you remove the very last line (the counsel-rg binding) things seem to work as they should. I don't understand what's causing this issue, and how to fix it.