Qt QML virtual keyboard not showing keys

[Iheb]

Hello,
I'm using Qt virtual keyboard on my application on LeMaker Guitar board. I used the basic virtual keyboard example to test it. The virtual keyboard show up. However, When I go to the digits page and go back to the alphabet page, the keys are not shown.
The image below show the problem. Why this is happening and how to solve it?

[ODБOï]

@Iheb hi
following informations can help people to help you :
Qt version
Compiler
Platform

[Iheb]

@LeLev hi, thank your for your reply. I'm using Qt 5.8.0 and cross compilation with gcc-linaro-7.4.1-2019.02-x86_64_arm-linux-gnueabihf compiler on Ubuntu Mate LeMaker Guitar board. My desktop OS is Ubuntu 16.04 LTS.