My X1C had serious problems with the first layer. I tried an older filament and a brand new PLA from Bambu. I followed all the recommended maintenance steps. It helped a little, but not much.
In the end it turned out to be the filament. I bought a Sunlu FilaDryer S2 and after drying everything worked perfectly again. I hadn’t thought about it because I had just taken the Bambu PLA out of the box.
If you have similar problems, try drying the filament; the X1C can do this without any additional equipment if necessary. Otherwise, I am very happy with the Sunlu S2.