I am experiencing the same issue after upgrade to 6.12.9.
It appears related to this Linux kernel commit:
https://github.com/torvalds/linux/commit/9815e39617541ef52d0dfac4be274ad378c6dc09
The commit attempts to correct over-enumeration of SATA ports, but it does not account for port multipliers that are common in a large number of SATA cards.
A reverse patch has been merged to the kernel tree, but it looks like Unraid must be using an affected kernel build. See: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=2f3c2b39768d2c0ccf0f6712a4b27453674e5de7
If an Unraid developer sees this, please investigate merging the patch into your kernel build and release an update. This is a critical failure for many people. Thanks!