Scaling problems with QT apps of ROS Melodic

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I'm having graphical issues with some parts of ROS QT apps (like RViz, Gazebo). Problems are:

• some number and text boxes do not fit their numbers
• scrollbars are tiny
• random visual artifacts

For example, here is the "pose creation" window of Moveit :

Tried changing QT env vars as per https://doc.qt.io/qt-5/highdpi.html
export QT_AUTO_SCREEN_SCALE_FACTOR='1'
export QT_SCALE_FACTOR='0.5, 0.8, 1.5, 2'
The second env var changes rendering but completely hides some parts of GUI.
I experience this issue only with ROS apps. VLC and other QT5 apps are fine.
I'm on a 14" FHD screen. Using Xubuntu 18.04 + i3.

Here is some additional info:

$ xrdb -query | grep -i dpi
Xft.dpi:    157

$ env | grep QT_
QT_QPA_PLATFORMTHEME=qt5ct
QT_ACCESSIBILITY=1

$ xdpyinfo | grep dots
resolution:    96x96 dots per inch

Unsetting QT_QPA_PLATFORMTHEME fixes the Path Constraints section alignment, but the moveit issue persists. I'm also using a size 10 font (set via QT5 Settings)