Steps to reproduce

Connect to remote ssh server via GNOME-Nautilus.

Drag-and-drop any file from Nautilius to Emacs or just open it from there.

Change this file and try to save.

Get the following Error

Saving file
/run/user/1000/gvfs/sftp:host=196.196.196.196,user=ubuntu/home/ubuntu/FOO...

basic-save-buffer-2: Unlocking file: Function not implemented,
/run/user/1000/gvfs/sftp:host=196.196.196.196,user=ubuntu/home/FOO


In GNU Emacs 27.0.50 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.22.30)
 of 2019-09-26 built on lcy01-amd64-022
Windowing system distributor 'The X.Org Foundation', version 11.0.11906000
System Description: Ubuntu 18.04.3 LTS

Recent messages:
(New file)
funcall-interactively: Buffer is read-only: #<buffer input> [3 times]
Making completion list...
delete-backward-char: Text is read-only
Making completion list...
Read-Only mode disabled in current buffer
Saving file /run/user/1000/gvfs/sftp:host=,user=ubuntu/home/ubuntu/input...
basic-save-buffer-2: Unlocking file: Function not implemented,
/run/user/1000/gvfs/sftp:host=,user=ubuntu/home/ubuntu/input
Mark set
Mark saved where search started

Configured using:
 'configure --build=x86_64-linux-gnu --prefix=/usr
 '--includedir=${prefix}/include' '--mandir=${prefix}/share/man'
 '--infodir=${prefix}/share/info' --sysconfdir=/etc --localstatedir=/var
 --disable-silent-rules '--libdir=${prefix}/lib/x86_64-linux-gnu'
 '--libexecdir=${prefix}/lib/x86_64-linux-gnu' --disable-maintainer-mode
 --disable-dependency-tracking --prefix=/usr --sharedstatedir=/var/lib
 --program-suffix=-snapshot --with-modules=yes --with-x=yes
 --with-x-toolkit=gtk3 --with-xwidgets=yes 'CFLAGS=-g -O2
 -fdebug-prefix-map=/build/emacs-snapshot-fC400k/emacs-snapshot-98514=.
-fstack-protector-strong
 -Wformat -Werror=format-security' 'CPPFLAGS=-Wdate-time
 -D_FORTIFY_SOURCE=2' 'LDFLAGS=-Wl,-Bsymbolic-functions -Wl,-z,relro''

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

Important settings:
  value of $LC_MONETARY: en_GB.UTF-8
  value of $LC_NUMERIC: en_GB.UTF-8
  value of $LC_TIME: en_GB.UTF-8
  value of $LANG: en_GB.UTF-8
  value of $XMODIFIERS: @im=ibus
  locale-coding-system: utf-8-unix

Major mode: Fundamental

Minor modes in effect:
  tooltip-mode: t
  global-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
  blink-cursor-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  buffer-read-only: t
  line-number-mode: t
  transient-mark-mode: t

Load-path shadows:
/usr/share/emacs/site-lisp/dictionaries-common/flyspell hides
/usr/share/emacs/27.0.50/lisp/textmodes/flyspell
/usr/share/emacs/site-lisp/rst hides
/usr/share/emacs/27.0.50/lisp/textmodes/rst
/usr/share/emacs/site-lisp/dictionaries-common/ispell hides
/usr/share/emacs/27.0.50/lisp/textmodes/ispell
/usr/share/emacs/site-lisp/latex-cjk-thai/thai-word hides
/usr/share/emacs/27.0.50/lisp/language/thai-word

Features:
(shadow sort mail-extr emacsbug message rmc puny dired dired-loaddefs
format-spec rfc822 mml easymenu mml-sec password-cache epa derived epg
epg-config gnus-util rmail rmail-loaddefs text-property-search seq
byte-opt gv bytecomp byte-compile cconv mm-decode mm-bodies mm-encode
mail-parse rfc2231 mailabbrev gmm-utils mailheader sendmail rfc2047
rfc2045 ietf-drums mm-util mail-prsvr mail-utils misearch multi-isearch
time-date subr-x cl-loaddefs cl-lib browse-url 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 menu-bar rfn-eshadow isearch timer select
scroll-bar mouse jit-lock font-lock syntax facemenu font-core
term/tty-colors frame 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 minibuffer 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 xwidget-internal move-toolbar
gtk x-toolkit x multi-tty make-network-process emacs)

Memory information:
((conses 16 49492 11491)
 (symbols 48 6177 1)
 (strings 32 16257 1599)
 (string-bytes 1 525839)
 (vectors 16 9447)
 (vector-slots 8 125910 11864)
 (floats 8 20 46)
 (intervals 56 291 0)
 (buffers 992 14))