Elegoo Neptune 4 Bed Warping

The Problem

My Elegoo Neptune 4, which has been in service about two months, is becoming very unreliable when printing larger objects (around 200mm in any axis). So, I’ve been tinkering with bed leveling and even writing a macro to heat soak the bed to 80C for 10 minutes before calibrating and saving the calibration. I’ve also doubled the resolution of the calibration from 5 to 10 points on each axis to get a better look at the shape of the bed.

The bed has developed what appears to be a wave shape based on the visualization in the Tuning panel of Fluidd. This is backed up by the physical results when printing as the areas that are lower on the visualization show lower adhesion, typically with the filament refusing to stick and being pulled off the bed only to start sticking again when the nozzle reaches the higher parts of the bed. This happens with both PLA and PETG, although I haven’t had issues with TPU. I’m also printing the initial layer at 10mm/s.

The Calibration Macro

[gcode_macro PREHEAT_BED_WAIT_CALIBRATE]
description: Preheats the bed, then waits, then calibrates
gcode: 
  M118  [PREHEAT_BED_WAIT_CALIBRATE] Pre-heating bed.
  M190 S80 ;Wait for the bed to reach print temp
  M118 [PREHEAT_BED_WAIT_CALIBRATE] Bed Pre-heated.
  M118 [PREHEAT_BED_WAIT_CALIBRATE] Calibration will begin in 10 minutes.
  G4 P600000; Wait 10 minutes, then calibrate
  M118 [PREHEAT_BED_WAIT_CALIBRATE] 10 Minutes Elapsed
  G29
  M118 [PREHEAT_BED_WAIT_CALIBRATE] Calibration…