FWIW, my issues were finally sorted with a replacement carbon rods gantry (a nightmare to install), and new extruder gears (after almost 4,000 hours, my original set was VERY worn).
Though I still run cleaner filament through the machine every week or so, and also do a factory reset after FW updates.
Okay, I can confirm, mine was the same issue. They sent me new carbon rods, which werenāt too bad to install (belts were a pain to remove), and after ~5 hours it is printing smooth layers again. It is also significantly quieter than it has ever been. Iām wondering if mine was defective from day 1 and I just never knew.
Only advice I can give anyone who has to do the same replacement, organize your hardware as you remove it. I literally put every section in separate baggies and still managed to lose 1 bolt. Luckily I had a spare.
Same for me - I found this post when trying to diagnose poor top layer quality. Printer only has 90 hours on. Went through all the cleaning, maintenance and calibration steps. Eventually identified issue with the carbon rods, are sending replacement.
I have been fighting similar top layer issues. I cam across this thread. Tried all of the listed suggestions. Then finally got to the bottom of the thread. So my question is pretty simple. If Bambu knows there is an issue with the carbon rods. It seems like the support shouldnāt be jerking my chain. And giving me all the standard pre typed responses. If they are tracking serial numbers of machines with a problem? I wonder if a trend is appearing. I had planned on buying a few of these machines. After the support response. I am starting to wonder if thatās a bad idea. Bambu, if you know itās a potential problem. Why not be transparent about it.
Hey, i had the same problem, it looked like in the pictures of drazel and nickam1025.
I have set the wrong nozzle size, 0,6 instead of 0,2 
.ridiculousā¦
@timidimage @nickam1025 @rdewsbery
How did you manage to convince bambu to send you the needed replacement parts? I struggled for weeks, sent almost 10gb of data (logs, projects, videos, photosā¦ ). a nightmare. couldnāt solve my problems (looks identical) and gave up.
Thereās still hopeā¦ 
I just sent them images of the layers. They had me run a few tests, then sent me gcode to run. After running the tests/gcode, I sent them the logs and they determined it was the Carbon Rods. Mine was still inside the year warranty.
Thanks for sharing. Any chance you could share the gcode with me? Iād like to understand what they were testing. Appreciated.
The forums donāt allow me to upload gcode but the link they sent me seems to still work.
In order to run this you need to put it on an SD Card and run it directly on the printer.
Insane. Thanks a million. Really great! 