Suffer disaster, as do envelopes that open in transit (4,7)
I believe the answer is:
come unstuck
'envelopes that open in transit' is the definition.
I know nothing about this answer so I can't judge whether this works.
'suffer disaster as do' is the wordplay.
I cannot quite see how this works, but
'do' could be 'come' (synonyms) and 'come' is present in the answer.
The remaining letters 'unstuck' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for come unstuck that I've seen before include "detached?" , "experience a setback?" , "Lose one's grip" , "Fail" , "Suffer failure" .)