Composed with the following character(s) "́" using this font:
  xfthb:-PfEd-DejaVu Sans Mono-normal-normal-normal-*-22-*-*-*-m-0-iso10646-1
by these glyphs:
  [0 1 1071 878 13 0 13 16 0 nil]
  [0 1 769 649 13 4 11 17 -13 [0 0 0]]
In 27.1 (x86_64-pc-linux-gnu, GTK+ Version 3.24.20)
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 LIBSYSTEMD JSON
PDUMPER LCMS2 GMP

It seems in 26.3 it's correct because it uses XFT, but the problem in 27.1
is with HarfBuzz .  Maybe HarfBuzz doesn't support combining accents on
some characters?  It fails with the scripts above, but still has no problems
with plain Latin characters.