After releasing CRYENGINE 5.5.1 we identified an issue affecting the Engine when it was downloaded via the CRYENGINE Launcher - this issue has been rectified in release 5.5.2. While we are confident that the problem has been resolved, should you encounter any further problems then please let us know through the usual channels.
Engine versions are now available through the CRYENGINE Launcher.
Sandbox Editor source code is only available via Github: https://github.com/CRYTEK/CRYENGINE