Description of problem:
With GNOME 3.26, the management of monitor scaling factors was moved from a global setting (managed either directly via the gsettings entry, or via GNOME Tweak Tool -> Window -> Scaling factor) to the Settings app. Changing this setting the old way is incompatible with how the scaling is managed in GNOME 3.26, so not having rebased GNOME Tweak Tool (which removed the scaling factor tweakability in 3.26) makes it easy to mess HiDPI support up.
Version-Release number of selected component (if applicable):
Since the tweak tool doesn't allow to "reset" the scaling factor, to get rid of the problem after having tweaked, the user must change back the org.gnome.desktop.interface scaling-factor setting to 0.
Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.
For information on the advisory, and where to find the updated
files, follow the link below.
If the solution does not work for you, open a new bug report.