# Waits a while so spinning rust disk has time to spin up boot_delay=10I have this same issue, which, like the OP, did not manifest when the external drive was an SSD. Now that it is a spinning disk (that tends to spin down when idle), I have the same problem with the OS not finding the boot drive when booting and so I have to specify it manually. In my case, I am specifying a wedge in my cmdline.txt file, not the underlying partitions.
While this should be addressed by NetBSD at some point, I've solved this by updating the firmware in the USB-SATA bridge, as written about here:
https://www.reddit.com/r/raspberry_pi/comments/a6ndx0/review_of_suptronics_x830/ Perhaps you can find something similar for yours. John