There is something wrong with the 1st 16M on your emmc
With a bootable uSD, it should "just boot" it (with mrfixits' stock debian,,1st 16M)
So, as I had to advise my son, like so
(and I am assuming that you know how to use dd)
Boot uSD, recent stock(mrfixit),, whether anything on emmc is mounted, doesn't matter
save emmc mbr (bs=512 count=1 of=emmc.mbr,,, some current directory on SD)
write 16M from SD to emmc (bs=1M count=16)
restore emmc mbr (if=emmc.mbr of=emmc,,, since only 512Bytes no count or bs needed)
--edit-- please note that Auyfans' images prioritize the emmc over SD,,
you may wish to do this for them too
--edit-- actually the SD does not need to be booted, just available, any boot will do,
but often the emmc is screwed up, the 1st 16M could be pulled off a suitable usb
(stock image dd'd to a usb stick)
With a bootable uSD, it should "just boot" it (with mrfixits' stock debian,,1st 16M)
So, as I had to advise my son, like so
(and I am assuming that you know how to use dd)
Boot uSD, recent stock(mrfixit),, whether anything on emmc is mounted, doesn't matter
save emmc mbr (bs=512 count=1 of=emmc.mbr,,, some current directory on SD)
write 16M from SD to emmc (bs=1M count=16)
restore emmc mbr (if=emmc.mbr of=emmc,,, since only 512Bytes no count or bs needed)
--edit-- please note that Auyfans' images prioritize the emmc over SD,,
you may wish to do this for them too
--edit-- actually the SD does not need to be booted, just available, any boot will do,
but often the emmc is screwed up, the 1st 16M could be pulled off a suitable usb
(stock image dd'd to a usb stick)