The two meals may have experienced different interruptions. Frequent access to one cavity changes its conditions without proving that its heater performs worse.
What the observation means
Basting a roast, checking a cake and leaving the other oven closed are not equivalent uses. The cavity size and door-opening duration further affect the comparison.
A useful next step
Keep the sequence with your notes and follow appropriate checking instructions for the food. Do not repeatedly open both ovens to create an artificial comparison. If one cavity remains unreliable under ordinary approved use, report its particular mode, loading and outcome for assessment.
Manuals and supporting guidance
Model-specific instructions take priority. These references support the practical principles discussed here; they do not diagnose your appliance.