I have been using this printer for years, random CoreXY kit, 8-bit Melzi board, generic MK8-style bowden hotend, heated bed, driven by Marlin 1.1.9 with Unified bed leveling enabled.
Last print several weeks ago was fine, did not at all adjust the hardware, but now it's air-printing the first layer. Redid the leveling (manual 16-point mesh spaced using a 0.15mm depth gauge) and there was no improvement. Thought I might have messed up something in Cura's gcode preamble section, so I printed an older file that worked fine previously, same problem. Display shows 0.24 mm height when first layer starts, which matches Cura's settings (though I'm not sure if that should change when bed level is on?). Changing "Bed Z" setting appears to have no effect, but I don't think I've used it since turning on bed leveling. The Z endstop adjustment is fine and will happily let the nozzle dig into the bed if requested.
If I run the leveling routine, I feel like it should negate any other factors since it knows where the bed is "now". So what the heck am I missing here that is throwing it off?
