820-00840 No spill. Not recognizing SSD's intermittently.

[bjf]

This board has no sign of a spill. SSD will sometimes work fine and I'm able to clone it and even boot to it. And then randomly, and fairly often, it will turn on to the question mark folder, or if I option-boot, there the SSD will not show up as an option. I've tried 3 known-good 2017 SSD's and they all behave identically. Any ideas?

 

[2informaticos]

Check J8600, U8640 and nearest components.
Be sure both L8600/02 are OK.
Resolder all components there, and pay atention to J8600 terminals.