Hi Stian,
Can you please contact you account representative and ask for this information?
Not sure if there is any reason why MTBF for these platforms is not available while for other it is.
Until that will be publicly available, I guess it's better to ask the account representative.
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If this worked for you please flag my post as an "Accepted Solution" so others can benefit. A kudo would be cool if you think I earned it.