Did Radxa ever iron out the heat sink issue with the X4? IIRC, when released, the official heat sink needed shimming to make proper contact with the processor.
For mine, following Explaining Computers' advice, I put in a copper shim, and that solved the issue. But I'm not sure if they ever sold through the stock of their first revision heatsink. I think they did, but I haven't bought another since the first two.