I haven't dealt with it in the GLA but a few other vehicles over the years. Oil contamination and/or a faulty filter-valve "pickup tube" typical culprits.
There's a reason
@Wayne , myself, and many others change oil/filter more often than the Benz maintenance checklist.
But also if you often track or otherwise spirited drive your AMG, especially with many aggressive turns, the sump may be starved of oil at a point and more readily ingest contaminants. I'm sure
@Wayne will now discuss the physics-advantages of a Porsche "dry sump", of which he is very well qualified.
