Extroot on RB750Gr3, loading wrong modules at boot?

I've been trying to follow Extroot configuration on my MikroTik RB750Gr3 without much success. I've got the SD card configured and can copy files to/from it just fine. The problem seems to be, when loading modules during pre-boot, something is failing causing extroot to not work.

[    7.779043] mount_root: loading kmods from internal overlay
[    8.193430] kmodloader: failed to open /tmp/overlay/upper/lib/modules/5.4.143/xhci-hcd.ko
[    8.202007] kmodloader: failed to open /tmp/overlay/upper/lib/modules/5.4.143/xhci-mtk.ko
[    8.210530] kmodloader: failed to open /tmp/overlay/upper/lib/modules/5.4.143/xhci-pci.ko
[    8.219095] kmodloader: failed to open /tmp/overlay/upper/lib/modules/5.4.143/xhci-plat-hcd.ko
[    8.264626] mount_root: failed to launch kmodloader from internal overlay
[    8.443393] block: attempting to load /tmp/jffs_cfg/upper/etc/config/fstab
[    8.512286] block: extroot: device not present, retrying in 15 seconds

Then, later, when modules.d loaded - things are great! But unfortunately, it fell back to the JFFS2 filesystem before that.

[   23.656900] block: extroot: cannot find device mmcblk0p1
[   23.663547] mount_root: switching to jffs2 overlay
[   25.758223] kmodloader: done loading kernel modules from /etc/modules.d/*
[   26.159171] mmc0: new high speed SDHC card at address 09b1
[   26.169444] mmcblk0: mmc0:09b1 SD16G 14.9 GiB 
[   26.184155]  mmcblk0: p1

I have the following symlinks:

lrwxrwxrwx    1 root     root            16 Oct 10 15:06 mmc -> ../modules.d/mmc
lrwxrwxrwx    1 root     root            25 Oct 10 16:20 sdhci-mt7620 -> ../modules.d/sdhci-mt7620


root@hex-router:/etc/modules-boot.d# ls mm*  | xargs cat
root@hex-router:/etc/modules-boot.d# ls sd*  | xargs cat

A similar problem that required a custom image: Usb-storage fail to load in preinit. Is that required here as well to get these into the /rom partition somehow?