Pi reading wrong USB stick when rebooting

It’s probably the old problem of identifying the USB stick.
The boot parameters (used to be in /boot/cmdline.txt, and still appear to be) need to be adjusted to bet the correct device.
I think I’ve seen a posting suggesting using the UUID.
Alternatively you would need to boot with the 2 USB stikc in various slots until you find which is the ‘first’

later: found the older post here which suggests PARTUUID might work, but didn’t see any confirmation of this.
HTH
Derek