1GB is the bare medium for the kiosk to run.
But sent a log it might reveal someting.
Generate a log:
goto <your-devices-IP-Address>/dev
Copy and paste the URL in this topic.
I have it running with the same WS 7.9" HDMI screen on a rPi4/4GB.
What is the output of:
cat /boot/userconfig.txt
cat /boot/config.txt
cat /boot/volumioconfig.txt