Sudden rippling in surface on Bambu X1C

I’m using a Bambu X1C with Bambu slicer.

Previously, I’ve never had these issues. Same printer, same model, same settings, and filament. But recently, the prints have consistently come out with what looks like VFAs.

I’ve cleaned the carbon rods, performed tensioning, full calibration, and lubricated the lead screws.

I’ve also lowered the flow rate down to 0.9, and increased the volumetric speed up from 12mm3/s to 18mm3/s. But the surface ripples still show up. Always in the same areas too.

I’m printing with NonOilen filament. Bed adhesion and all other surface comes out perfect.

Has anyone found a solution to this seemingly well known/common problem?

I will try lowering flow rate some more, and decreasing volumetric speed to 8mm3/s

What else can I try?