There might also be some variances in components between units (different manufacturers, batches, etc..) that might have been "uncovered" by some minor change in kernel code.
I remember having a unit of Rock Pi 4A (no wifi) that did not boot with eMMC while the other unit 4GB 4B (wifi) did boot without issues.
I consulted other Rock Pi 4A Armbian users and they did not observe such behaviour.
I finally found the cause in the mmc kernel driver and even implemented a patch for it in Armbian, but that did require lots of fiddling and debugging.
Unfortunately at this point I cannot reproduce the issue with my NanoPi R4S unit.
There might also be some variances in components between units (different manufacturers, batches, etc..) that might have been "uncovered" by some minor change in kernel code. I remember having a unit of Rock Pi 4A (no wifi) that did not boot with eMMC while the other unit 4GB 4B (wifi) did boot without issues. I consulted other Rock Pi 4A Armbian users and they did not observe such behaviour. I finally found the cause in the mmc kernel driver and even implemented a patch for it in Armbian, but that did require lots of fiddling and debugging. Unfortunately at this point I cannot reproduce the issue with my NanoPi R4S unit.