The Chromebox is standard intel hardware. So 'Generic' will work fine. What other image did you use to install LE on the new Chromebox and in which way do they differ?
Here is a video which shows the steps to be done to migrate from OE to LE.
HOW TO:Update LibreELEC - LibreELEC
There MUST be an 'update' folder. Connect to it like shown in the video above and use the generic build.