Following the coffee tutorial, managed to get it working, but now, all of the sudden it seems that part of the liquid is not behaving the right way, anyone know what might be the issue here?
The normals on your cup object are flipped inside out. You can see this by selecting the “Face Orientation” viewport overlay, which displays the front side of faces in blue and the back side in red:
To fix this, in Edit Mode, select all your cup’s faces, then press ShiftN to recalculate the normals so they point outside the mesh. This fixes the rendering issue.