Troubleshooting nvme0 and nvme1 slots on Framework 16

Hi, trying to troubleshoot. On the FW16, which storage slots correspond respectively to the nvme0 and nvme1 labels? Some guides indicate that nvme0 is primary storage. Others indicate that nvme0 is secondary storage.

Sometimes when I log in, if I run mount | grep " / " it returns /dev/nvme1n1p2. Other login sessions if I run the same command it returns /dev/nvme0n1p2 instead. Is this expected or normal behavior for the FW16? What are the probable causes?

OS: Ubuntu 24.04.1
BIOS version: 3.05