defining a function:
(defun xxx-insert()
 "anything" 
 (interactive)
 (insert "# Local Variables:\n")
 (insert "# mode: org\n")
 (insert "# End:\n")
 )
will cause Emacs to disregard the Emacs-lisp-mode after re-opening the file, hence no syntax
evaluation anymore
Changing (insert "# Local Variables:\n") to (insert "# Local Bariables:\n") will 'solve' the problem.
Note: exactly the same behaviour invoking emacs with -Q

In GNU Emacs 28.0.50 (build 58, x86_64-pc-linux-gnu, GTK+ Version 3.24.28, cairo version 1.16.0)
 of 2021-04-26 built on XYZ
Repository revision: 50f29f6a282b7426377be5fb54322fc5b5a487fc
Repository branch: master
Windowing system distributor 'Fedora Project', version 11.0.12011000
System Description: Fedora 33 (Thirty Three)
Configured using:
 'configure --prefix=/opt/emacs --sysconfdir=/etc
 --enable-locallisppath=/usr/local/share/emacs/site-lisp
 --libexecdir=/opt/emacs/lib/ --localstatedir=/usr/local/var
 --enable-largefile --with-x-toolkit=gtk3 --with-modules --with-xwidgets
 --without-pop --without-selinux --without-gnutls
 --with-file-notification=yes --with-json --with-cairo
 'CFLAGS=-march=native -Os''
Configured features:
ACL CAIRO DBUS FREETYPE GIF GLIB GMP GPM GSETTINGS HARFBUZZ JPEG JSON
LIBOTF LIBSYSTEMD LIBXML2 M17N_FLT MODULES NOTIFY INOTIFY PDUMPER PNG
RSVG SECCOMP SOUND THREADS TIFF TOOLKIT_SCROLL_BARS X11 XDBE XIM XPM
XWIDGETS GTK3 ZLIB
Important settings:
 value of $LANG: en_US.utf8
 value of $XMODIFIERS: @im=none
 locale-coding-system: utf-8-unix
Major mode: ELisp/d
Minor modes in effect:
 show-paren-mode: t
 recentf-mode: t
 desktop-save-mode: 1
 global-hl-line-mode: t
 hl-line-mode: t
 delete-selection-mode: t
 cua-mode: t
 flymake-mode: t
 savehist-mode: t
 global-auto-revert-mode: t
 auto-insert-mode: t
 tabbar-mwheel-mode: t
 tabbar-mode: t
 smooth-scroll-mode: t
 auto-complete-mode: t
 global-undo-tree-mode: t
 undo-tree-mode: t
 save-place-mode: t
 tooltip-mode: t
 global-eldoc-mode: t
 eldoc-mode: t
 electric-quote-mode: t
 electric-indent-mode: t
 mouse-wheel-mode: t
 tool-bar-mode: t
 global-prettify-symbols-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
 size-indication-mode: t
 column-number-mode: t
 line-number-mode: t
 global-visual-line-mode: t
 visual-line-mode: t
 transient-mark-mode: t
Load-path shadows:
None found.
Features:
(shadow sort mail-extr emacsbug sendmail ol-eww eww xdg url-queue mm-url
ol-rmail ol-mhe ol-irc ol-info ol-gnus nnselect gnus-search eieio-opt
speedbar ezimage dframe gnus-art mm-uu mml2015 mm-view mml-smime smime
dig gnus-sum shr kinsoku svg dom browse-url gnus-group gnus-undo
gnus-start gnus-dbus dbus xml gnus-cloud nnimap nnmail mail-source utf7
netrc nnoo parse-time gnus-spec gnus-int gnus-range message rmc puny
rfc822 mml mml-sec epa epg epg-config mm-decode mm-bodies mm-encode
mail-parse rfc2231 mailabbrev gmm-utils mailheader gnus-win gnus
nnheader gnus-util rmail rmail-loaddefs rfc2047 rfc2045 ietf-drums
mail-utils mm-util mail-prsvr ol-docview doc-view jka-compr image-mode
exif dired-sort-menu dired dired-loaddefs ol-bibtex bibtex iso8601
ol-bbdb ol-w3m pp default-daemon server executable cl-extra misearch
multi-isearch cursor-sensor ffap checkdoc lisp-mnt help-mode
user-profile default-gnus contrib/chartables powerline
powerline-separators powerline-themes default-profile default-ui paren
man recentf vc-dispatcher vc-svn desktop frameset avoid hl-line
default-faces default-keymap delsel cua-base facemenu default-run
default-restart default-modes default-platform default-unix
default-flymake default-flymake-go default-flymake-csharp
default-flymake-ruby default-flymake-js default-flymake-py
default-flymake-java default-flymake-shell flymake-proc flymake compile
text-property-search warnings default-run-assoc run-assoc default-tempo
default-tempo-rexx default-tempo-sh default-tempo-pas default-tempo-js
default-tempo-java default-tempo-perl default-tempo-elisp
default-tempo-c-cpp default-menu default-help default-options
default-tools default-search default-format default-view
aquamacs-cmm-menu default-edit default-file default-generic savehist
autorevert filenotify autoinsert default-functions default-autoload
nf-procmail-mode ox-man ox-odt rng-loc rng-uri rng-parse rng-match
rng-dt rng-util rng-pttrn nxml-parse nxml-ns nxml-enc xmltok nxml-util
ox-latex ox-icalendar ox-html table ox-ascii ox-publish ox org-element
org ob ob-tangle ob-ref ob-lob ob-table org-macro org-footnote org-src
ob-comint org-pcomplete pcomplete comint ansi-color ring org-list
org-faces org-entities time-date org-version ob-emacs-lisp org-table
org-keys org-loaddefs find-func cal-menu calendar cal-loaddefs avl-tree
generator ol ob-exp ob-core org-compat ob-eval org-macs format-spec
markdown-mode rx thingatpt noutline outline easy-mmode jison-mode
bison-mode cc-mode cc-fonts cc-guess cc-menus cc-cmds cc-styles cc-align
cc-engine cc-vars cc-defs flex-mode derived aquamacs-tabbar cus-load
aquamacs-tools tabbar restore-last-frame-size org-bullets syslog-mode
hide-lines web-mode disp-table vimrc-mode go-autocomplete
go-mode-autoloads neotree advice smooth-scroll aok fill-column-indicator
tempbuf auto-complete-config auto-complete edmacro kmacro undo-tree diff
multi-shell windata tree-mode tree-widget wid-edit imenu imenu-tree
tempo saveplace google-translate google-translate-default-ui
google-translate-core-ui color popup ido google-translate-core
google-translate-tk google-translate-backend url url-proxy url-privacy
url-expand url-methods url-history url-cookie url-domsuf url-util
url-parse auth-source cl-seq eieio eieio-core cl-macs eieio-loaddefs
password-cache url-vars mailcap cl-loaddefs cl-lib json subr-x map seq
byte-opt gv bytecomp byte-compile cconv eol-conversion default-path
iso-transl 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 easymenu timer select scroll-bar mouse jit-lock
font-lock syntax 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 button loaddefs faces cus-face macroexp files
window text-properties overlay sha1 md5 base64 format env code-pages
mule custom widget hashtable-print-readable backquote threads
xwidget-internal dbusbind inotify 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 327973 299086)
 (symbols 48 32950 2)
 (strings 32 117560 25908)
 (string-bytes 1 4009819)
 (vectors 16 61069)
 (vector-slots 8 1342703 309626)
 (floats 8 464 2216)
 (intervals 56 813 716)
 (buffers 992 16))