Please make sure you have followed the De'Longhi recommendation for best milk frothing, make sure your milk (or plant-based drink) is at fridge-temperature before using the LatteCrema Cool carafe.
In details:

• When using DAIRY milk, the best result in cup can be obtained when using skimmed milk (no-fat content) 
• PLANT-BASED drinks as a lower amount of fats compared to dairy, so the result in cup can vary depending on several factors, the plant-based brand and the type of plant-based in some of those. There are three main typologies of plant-based options that are ideal for frothing: oat, soy and almond*.

*Plant-based drinks might vary a lot from brand to brand, from type to type, as the list of ingredients often changes.