Thanks for posting your findings goathunter, I'm seeing the same problem. Very frustrating! Thanks for the tips on which versions work, now I know how far I can upgrade before I get the dreaded uuid message.
This is definitely a problem with 5.10.21 somehow. I'll spare you the details, but I managed to start fresh with 5.10.12, then upgraded to 5.10.16, and all was well. The MicroSD card could still be seen. Upgraded to 5.10.21, no more /dev/mmcblk0p1 device at all.
I'm now frozen at 5.10.16 for the time being, and everything is as it should be.
And to clarify, I do not see this problem with 5.10.21 on two PINE A64s (non-LTS) and on a RockPro64. Only the PINE A64-LTS (the SOPINE images) has the problem.
GregH got a reaction from goathunter in Pine A64 LTS boots from SD, but once booted, the SD device is MIA