What we tested

FilePrusaSlicer saidActual problemResult
Two 20 mm blocks, the second floating 5 mm above the firstEmpty layer between 10 and 15.2.2 separate parts, nothing between 10 and 15 mmG-code exported; the upper block starts in mid-air
Thingi10K 52310 by Typhoon69 (CC BY-SA)Empty layer between 10 and 10.8.1,334 open edges, 141 shells; FixSTL repaired it partlyWarnings remained after repair
PrusaSlicer 2.9.6, macOS, command line: --info gives the object-list statistics; slices used the defaults with a 0.4 mm nozzle, 0.2 mm layers, supports off. "Same filament" compares G-code from the original and from FixSTL's repair. Nothing was printed.

What is going on

The full warning adds the object name and "Make sure the object is printable. This is usually caused by negligibly small extrusions or by a faulty model. Try to repair the model or change its orientation on the bed." (source). Since 2.3 it is a warning rather than an error (release notes).

Bambu Studio refuses to slice the same file.

What was actually wrong

How to fix it

  1. Scrub the layer preview to the heights in the warning.
  2. Check the file in FixSTL for separate shells and large holes.
  3. Connect or lower the floating part in your modelling program, or split it into separate objects on the bed.
  4. Slice again and confirm the warning is gone before printing.

Source: Seen in our tests · PrusaSlicer 2.9.6 on macOS