I have many problems with sd cards too.
I will try to be brief
.
So when i flash Android to "MediaRange micro sd hc 16GB class10", at first boot it works very good and the system is very fast, but when i reboot my rock64 it's going immediatly to recovery... I must wipe the system completely then it boots like the first time.
With "SanDisk 16GB hc I class10" the system (android) is very slow ,but there is no problem at reboot.
With "Samsung 32GB evo+" it,s a little less slow...
So it really depends of sd card.
I will try to be brief

So when i flash Android to "MediaRange micro sd hc 16GB class10", at first boot it works very good and the system is very fast, but when i reboot my rock64 it's going immediatly to recovery... I must wipe the system completely then it boots like the first time.
With "SanDisk 16GB hc I class10" the system (android) is very slow ,but there is no problem at reboot.
With "Samsung 32GB evo+" it,s a little less slow...
So it really depends of sd card.