Development tools for Zephyr on STM32Workbench for Zephyr: VS Code extension to set up, build, flash and debug Zephyr applications on STM32.Devicetree manager: browse, edit and visualize Zephyr devicetree, STM32CubeMX-like for Zephyr.
This happend to me also. I am running Keppler on OSX. I quit Eclipse and restarted it and the problem went away.
Check the project C/C++ Build | Settings | MCU Settings | Path . Mine is ${openstm32_compile_path}