Recipe:
emacs -Q
M-x package-list-packages

error is printed: "wrong type argument: stringp treemacs"

When run with debug-on-error, the trace looks like this:
Debugger entered--Lisp error: (wrong-type-argument stringp treemacs)
   intern(treemacs)
   package-desc-from-define(treemacs "20201218.652" "A tree style file 
explorer package" '((emacs "25.2") (cl-lib "0.5") (dash "2.11.0") (s 
"1.12.0") (f "0.11.0") (ace-window "0.9.0") (pfuture "1.7") (hydra 
"0.13.2") (ht "2.2")) :commit "6b045fd585421ab3c9e1185c2508d34af700490b" 
:authors (("Alexander Miller" . "alexanderm@web.de")) :maintainer 
("Alexander Miller" . "alexanderm@web.de") :url 
"https://github.com/Alexander-Miller/treemacs")
   apply(package-desc-from-define (treemacs "20201218.652" "A tree style 
file explorer package" '((emacs "25.2") (cl-lib "0.5") (dash "2.11.0") 
(s "1.12.0") (f "0.11.0") (ace-window "0.9.0") (pfuture "1.7") (hydra 
"0.13.2") (ht "2.2")) :commit "6b045fd585421ab3c9e1185c2508d34af700490b" 
:authors (("Alexander Miller" . "alexanderm@web.de")) :maintainer 
("Alexander Miller" . "alexanderm@web.de") :url 
"https://github.com/Alexander-Miller/treemacs"))
   package-process-define-package((define-package treemacs 
"20201218.652" "A tree style file explorer package" '((emacs "25.2") 
(cl-lib "0.5") (dash "2.11.0") (s "1.12.0") (f "0.11.0") (ace-window 
"0.9.0") (pfuture "1.7") (hydra "0.13.2") (ht "2.2")) :commit 
"6b045fd585421ab3c9e1185c2508d34af700490b" :authors (("Alexander Miller" 
. "alexanderm@web.de")) :maintainer ("Alexander Miller" . 
"alexanderm@web.de") :url "https://github.com/Alexander-Miller/treemacs"))
package-load-descriptor("/home/eric/.emacs.d/elpa/treemacs-20201218.652")
   package-load-all-descriptors()
   package-initialize(t)
   package-list-packages()
   eval((package-list-packages) t)
   ielm-eval-input(#("(package-list-packages)" 0 23 (fontified t)) nil)
   ielm-send-input(nil)
   ielm-return()
   funcall-interactively(ielm-return)
   call-interactively(ielm-return nil nil)
   command-execute(ielm-return)

I have (package-initialize) in my init file so running without emacs -Q 
or -q just prints "wrong type arguement: stringp treemacs" to the 
console and exits. Running with --debug-init does not produce any other 
output.

In GNU Emacs 27.1 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.24.22, 
cairo version 1.17.3)
  of 2020-08-28 built on juergen
Windowing system distributor 'The X.Org Foundation', version 11.0.12010000
System Description: Arch Linux

Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.
package-desc-from-define: Wrong type argument: stringp, treemacs
delete-backward-char: Text is read-only

Configured using:
  'configure --prefix=/usr --sysconfdir=/etc --libexecdir=/usr/lib
  --localstatedir=/var --with-x-toolkit=gtk3 --with-xft --with-wide-int
  --with-modules --with-cairo --with-harfbuzz 'CFLAGS=-march=x86-64
  -mtune=generic -O2 -pipe -fno-plt' CPPFLAGS=-D_FORTIFY_SOURCE=2
  LDFLAGS=-Wl,-O1,--sort-common,--as-needed,-z,relro,-z,now'

Configured features:
XPM JPEG TIFF GIF PNG RSVG CAIRO SOUND GPM DBUS GSETTINGS GLIB NOTIFY
INOTIFY ACL GNUTLS LIBXML2 FREETYPE HARFBUZZ M17N_FLT LIBOTF ZLIB
TOOLKIT_SCROLL_BARS GTK3 X11 XDBE XIM MODULES THREADS LIBSYSTEMD JSON
PDUMPER LCMS2 GMP

Important settings:
   value of $LANG: en_US.UTF-8
   locale-coding-system: utf-8-unix

Major mode: Lisp Interaction

Minor modes in effect:
   tooltip-mode: t
   global-eldoc-mode: t
   eldoc-mode: t
   electric-indent-mode: t
   mouse-wheel-mode: t
   tool-bar-mode: t
   menu-bar-mode: t
   file-name-shadow-mode: t
   global-font-lock-mode: t
   font-lock-mode: t
   blink-cursor-mode: t
   auto-composition-mode: t
   auto-encryption-mode: t
   auto-compression-mode: t
   line-number-mode: t
   transient-mark-mode: t

Load-path shadows:
None found.

Features:
(shadow sort mail-extr emacsbug message rmc puny dired dired-loaddefs
format-spec rfc822 mml mml-sec epa derived epg epg-config gnus-util
rmail rmail-loaddefs text-property-search time-date mm-decode mm-bodies
mm-encode mail-parse rfc2231 mailabbrev gmm-utils mailheader sendmail
rfc2047 rfc2045 ietf-drums mm-util mail-prsvr mail-utils finder-inf
package easymenu browse-url url-handlers url-parse auth-source cl-seq
eieio eieio-core cl-macs eieio-loaddefs password-cache json subr-x map
url-vars seq byte-opt gv bytecomp byte-compile cconv cl-loaddefs cl-lib
tooltip eldoc electric uniquify ediff-hook vc-hooks lisp-float-type
mwheel term/x-win x-win term/common-win x-dnd tool-bar dnd fontset image
regexp-opt fringe tabulated-list replace newcomment text-mode elisp-mode
lisp-mode prog-mode register page tab-bar menu-bar rfn-eshadow isearch
timer select scroll-bar mouse jit-lock font-lock syntax facemenu
font-core term/tty-colors frame minibuffer cl-generic cham georgian
utf-8-lang misc-lang vietnamese tibetan thai tai-viet lao korean
japanese eucjp-ms cp51932 hebrew greek romanian slovak czech european
ethiopic indian cyrillic chinese composite charscript charprop
case-table epa-hook jka-cmpr-hook help simple abbrev obarray
cl-preloaded nadvice loaddefs button faces cus-face macroexp files
text-properties overlay sha1 md5 base64 format env code-pages mule
custom widget hashtable-print-readable backquote threads dbusbind
inotify lcms2 dynamic-setting system-font-setting font-render-setting
cairo move-toolbar gtk x-toolkit x multi-tty make-network-process emacs)

Memory information:
((conses 16 63942 11613)
  (symbols 48 7861 1)
  (strings 32 22240 1754)
  (string-bytes 1 705414)
  (vectors 16 13131)
  (vector-slots 8 164344 13722)
  (floats 8 21 27)
  (intervals 56 201 0)
  (buffers 1000 11))