Is the Rock 64 something strange?

[stuartiannaylor]

In this case, should we suspect hardware (Rock 64)?

No.

... always suspect a bad, cheap, defective or fraudulent SD card;  its that simple.

We recommend Samsung 32G Class 10 Evo Plus cards !   Also, you can test your cards for fraud;  there are many fraudulent cards out there;  please read this link.

Thanks for the reply.

Is Samsung EVO plus? If EVO is useless, I feel pretty severe with regard to the corresponding microsd.
Let's buy Evo plus for the time being and try it.

Best regards.

Evo is OK but beware there are a huge amount of counterfeits on offer or sub standard product.
Evo just slower and the price saving isn't really worth while but that card you have could be defective.
Have you tried writing an number of large files to it and used it on something else?