I have had some issues trying to boot from eMMC with the last version of Armbian (kernel v5.4) while it's working perfectly on Armbian with a v4.4 kernel.
Images not working:
I though I messed up with the SPI or the eMMC card but after trying all I could, it finally worked using an old version of Armbian.
The new images are working on a SD-Card but it's much slower to boot.
On a eMMC card it get completely stuck (see attached file), I managed to get the "Done" displayed waiting much longer (just after the "Running /scripts/local-premount" step but nothing more).
The CPU is becoming super hot while it stuck.
I have the same issue on two different RockPro64 cards and with two different eMMC cards.
I have tried the "Disable SPI while booting" step but it didn't help:
It would be great if I could have a kernel 5.4 running on eMMC on those cards, please let me know if I can help.