Resolved! STM32MP157 Errata 2.3.8, "eMMC boot Timeout too short", causes problems with available eMMCs.
The STM32MP157 demands a maximum time of 10 ms from reset command to boot partition data. According to JEDEC No 84-B51 the maximum time from reset command to the first data is up to 1 second (tBD):All data sheets of eMMCs that I found specify their b...