sounds like your infill is not laying as it should be leading to build up / spikes which ruin your surface.
why is it not sticking? could be many reasons and will take some testing to see how to fix it. some things i would try:
- instead of using stock settings you could try and tune using the orca slicer using instructions here ( PSA: START HERE! Calibration made SIMPLE & please SHARE User Tips! - Bambu Lab Software - Bambu Lab Community Forum ) sometimes even a change in color in the same filament base material can cause deviations
- try bumping up the nozzle temp maybe 5c at a time
- try reducing cooling
- slow down your print
- see if you can reproduce the problem on a small print, like a calibration cube type of print. this way you can iterate quickly to try different settings