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.