Pressure changes or the appliance's internal arrangement may contribute on some designs, but the door must still settle into its intended closed position. Persistent opening is not something to ignore.
What the observation tells you
A slam creates a different event from gentle closure and can hide a loading or alignment problem. Check for contents obstructing the second door through ordinary access. Do not add a latch to force it shut without understanding the cause.
A useful next step
Use gentle normal closure and note whether the other door remains open. Report repeated gaps, frost or temperature changes for model-specific assessment.
Manuals and supporting guidance
Model-specific instructions take priority. These references support the practical principles discussed here; they do not diagnose your appliance.