Since 14. March 2019 old images (up to V7) based on Raspbian/Debian Jessie started to show wrong icons and also other functions requiring downloads do not show the expected views on the touchscreen.
This is not a Repetier-Server error. Our analysis shows that the uBlock Origin Extension in chromium is broken somehow. It adds 100% load and does not resolve.
As a solution you can simply delete this extension. Login over ssh and send:
rm -r /home/pi/.config/chromium/Default/Extensions/cjpalhdlnbpafiamejdnhcphjbkeiagm sudo reboot
After restart the icons and all functions should be back as it used to be.