Fstab entry changes device name

Pulling my hair out with this one (although I have learned a lot about maintenance mode!)

I install Lubuntu onto my notebook hard drive, and the partition gets the label /dev/mmcblk0p1.

I add an internal SD card. It gets the label /dev/mmcblk1p1, and is mounted at /home/<userid>/<uuid>.

I can unmount it, and mount it at /mnt. Everything is good.

If I add a line to /etc/fstab to mount the SD card, it switches to /dev/mmcblk0p1, with the root partition now being /dev/mmcblk1p1. Naturally a bunch of things stop working.

Doesn't matter whether I reference the SD device name (*) or the uuid in fstab, nor whether I put it at the start or the end of the entries.

I don't understand what's happening. It doesn't matter whether I install Lubuntu with or without the SD card in place (I have tried several routes).

*** UPDATE ***

Lubuntu 22.04.

Having gone back to the original fstab, and taken out the SD card, the boot partition remains at /dev/mmcblk1 and I still have issues with PulseAudio, for example (exclamation mark in the system tray and upon opening PusleAudio I get "Establishing connection to PulseAudio. Please wait ...")

It all seems highly non-deterministic, but I have no doubt it's just about finding the right config file or doing things in the right order.

I notice I also now have a new version at the grub loader, which appeared without any action on my part (computer was in sleep mode and the new version was there upon restart).

Original fstab:

# /etc/fstab: static file system information.## Use 'blkid' to print the universally unique identifier for a device; this may# be used with UUID= as a more robust way to name devices that works even if# disks are added and removed. See fstab(5).## <file system>             <mount point>  <type>  <options>  <dump>  <pass>UUID=73BA-4094                            /boot/efi      vfat   umask=0077 0 2 UUID=525a30ce-ac82-4ab3-9ded-38a4b5cc6f80 /             ext4    defaults,discard 0 1 tmpfs                                     /tmp           tmpfs   defaults,noatime,mode=1777 0 0

Revised fstab:

# /etc/fstab: static file system information.## Use 'blkid' to print the universally unique identifier for a device; this may# be used with UUID= as a more robust way to name devices that works even if# disks are added and removed. See fstab(5).## <file system>             <mount point>  <type>  <options>  <dump>  <pass> UUID=73BA-4094                            /boot/efi      vfat   umask=0077 0 2 UUID=525a30ce-ac82-4ab3-9ded-38a4b5cc6f80 /             ext4    defaults,discard 0 1 tmpfs                                     /tmp           tmpfs   defaults,noatime,mode=1777 0 0 UUID=26ADD53F795460BB                     /mnt           ntfs    defaults 0 0