Emacs 26.3 strange ESS init error regarding Projectile and project root.

[Carlo Tambuatco]

I have both ESS and projectile installed and I have projectile mode on by
default.

>From my init.el file:

;; Load projectile
(use-package projectile
  :ensure t
  :config
  (define-key projectile-mode-map (kbd "C-x p") 'projectile-command-map)
  (projectile-mode +1))

Recently (as of about 1 day ago), emacs has been giving me this error
when call (require 'ess-site) in my ESS-init.el file, or whenever I try to
open an interactive R session via M-x R

"project-root is already defined as something else than a generic function."

WTF....?

Maybe it will help if I include some debugging output:

Begin Error:
-------------------------------------------------------------------------------------------------------------
Debugger entered--Lisp error: (error "project-root is already defined as
something else than a generic function")
  signal(error ("project-root is already defined as something else than a
generic function"))
  error("%s is already defined as something else than a generic function"
project-root)
  cl-generic-ensure-function(project-root)
  cl-generic-define-method(project-root nil ((project (head
ess-r-package))) nil #f(compiled-function (project) "Return the project
root for ESS R packages" #<bytecode 0x13a9d4d>))
  byte-code("\300\301\302\303\302\304%\210\300\305\302\306\302\307%\207"
[cl-generic-define-method project-roots nil ((project (head
ess-r-package))) #f(compiled-function (project) "Return the project root
for ESS R packages" #<bytecode 0x13a9d41>) project-root ((project (head
ess-r-package))) #f(compiled-function (project) "Return the project root
for ESS R packages" #<bytecode 0x13a9d4d>)] 6)
  require(ess-r-package)
  eval-buffer(#<buffer  *load*-836759> nil
"/home/carlotam79/.emacs.d/elpa/ess-20210520.2146/ess-r-mode.el" nil t)  ;
Reading at buffer position 1277

load-with-code-conversion("/home/carlotam79/.emacs.d/elpa/ess-20210520.2146/ess-r-mode.el"
"/home/carlotam79/.emacs.d/elpa/ess-20210520.2146/ess-r-mode.el" nil t)
  require(ess-r-mode)
  eval-buffer(#<buffer  *load*> nil
"/home/carlotam79/.emacs.d/elpa/ess-20210520.2146/ess-site.el" nil t)  ;
Reading at buffer position 2217

load-with-code-conversion("/home/carlotam79/.emacs.d/elpa/ess-20210520.2146/ess-site.el"
"/home/carlotam79/.emacs.d/elpa/ess-20210520.2146/ess-site.el" nil t)
  require(ess-site)
  (progn (require (quote ess-site)))
  eval((progn (require (quote ess-site))) t)
  elisp--eval-last-sexp(nil)
  eval-last-sexp(nil)
  funcall-interactively(eval-last-sexp nil)
  call-interactively(eval-last-sexp nil nil)
  command-execute(eval-last-sexp)
---------------------------------------------------------------------------------------------------------------------
End error

I feel like this might be fixed by setting some environment variable in
either projectile or ESS,
but this error message is not helping me to figure it out...