Of course, [my trouble-shooting strategy] is all premised upon devising a stimulus that reliably
reproduces the result. When my HDD's/SSD's were having SATA cable
and/or drive rack problems, reading 10 GB from them typically produced
at least one error.
I cannot comment on that, I very very rarely have [SATA UDMA CRC] issues.
Last time I had it turned out to be faulty RAM (very rare bit rots), not
SATA cable.
When the OP read 10 GB of the SSD using the d-i rescue shell, he was
applying a stimulus after changing the variable "OS instance". The
result was different. Therefore, the SATA UDMA CRC errors are related
to changing the OS instance
Maybe. But my bet this is hardware error. RAM or SATA Cable, or SSD
itself. Or motherboard, then this is dead in the water and laptop would
need to be recycled/sold as spares if this happens.
I would also suggest to OP at this point, to do full memtest86 by
passmark (UEFI only) https://www.memtest86.com/
Or old typical (but bugged sometimes) memtest86+ https://www.memtest.org/
Full run of either to make sure CPU/RAM is good.