Bed leveling issue can be caused by:
1) Build platform wobbly
Check wheels under the build platform, if any of them can be spin freely, adjust the eccentric nut, just thight enough to eliminate the wobbly bed. Push the bed, if you feel it is bumpy when moving, this is the sign of the one or more wheels are too tight, adjust again.
2) V slot / POM wheel worn out
Replace the POM wheel will help
3) Aluminium extrusion twisted (rare)
No matter how you adjust the knob underneath the build platform, the diagonal conner of the bed aew unable to be leveled properly. Contact the shop where you bought the printer from, if it’s still under warranty, ask for replacement of the Y axis aluminium extrusion.
