How do the problems go away? Is the lifespan of the built in eMMC longer compared to a high quality wear leveling sd-card? I am a layman, but isn’t the problem the flash which should be basically the same?

An SD card is using contact pins to make the connection, which is susceptible to dirt and vibration. eMMC is soldered to the board so you no-longer need to worry about environmental and mechanical disturbances.

The eMMC has a known supply chain and is guaranteed for 1 million write cycles that are then wear leveled. The SD card could be coming from anywhere, or a counterfeit with who knows how many write cycles and wear leveling.

The CMs are built for industrial use and I've shipped a few products based on them, shipping thousands of units. They have had zero flash failures.

Thanks for elaborating, valuable advice.

Not even NOR SLC flashes are regularly specified for 1 million erase cycles. And common MLC/TLC eMMCs certainly are not. What are you talking about? :)