So, Why my second mini0806 was always crashing?
Turns out to be it was the internal cable after all.
Update: it was still crashing (differently), so cable was not the ultimate problem. I didn’t figured out the problem as camera is dead now from a relatively soft drop.
Here is the fix:
hot glue for a good measure:
The original cable:
I used some telephone/Cat5 cable due to lack of better alternative, it works good now.
I also noticed a peculiar thing: card slot A and slot B have different read/write speeds.