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That is an unusual solution for such a problem and I don't have an initial idea about the root cause based on what is presented, so here are some questions / tasks to try out.
First question is when you say the device does not start up, does that mean it is held in reset? Or does it get trapped in a fault?
If it is not clear, then you can look the reset cause register to find out and in general it would be good to understand what is indicated in that register.
Another question is can you do an AB-BA swap since you have so many good boards? Given how unusual the solution is to solve this and not having seen issues with SSI hardware connections before, my gut instinct is maybe a board level issue, so an AB-BA swap would help indicate if the issue follows the IC or if it's isolated on the board. That would help better target the debug efforts.
Lastly you mentioned the SD card being installed brings the boards up, does that mean:
I suppose it runs in a fault, but not 100% sure (we measure 30% less current of the board when the bug appears)
we will check the reset cause register this week
we will try an AB-BA swap, when the next board with this fault will appear.
Yes. it is "or" we can use the SD or we can sold the Pull-Up
br Ralf and thanks for your suggestions!