RE: Print issue only when setting Infill to Lightning ... Bug or not Bug ?
Would need your project file to check settings and preview the slice but it’s also quite possible that you just don’t have the % set high enough to provide sufficient support for the flat areas. This is quite a common occurrence with many/most of the support patterns. The lower the percentage the more top layers are usually needed to compensate for the surface sagging between the supports.
RE:
Hard to comment with any confidence without seeing the 3mf project file but I suspect, density of infill is not enough to support a flat horizontal surface. I'd try something like 25% gyroid or cubic. Also depends on how many top layers, but again, without the 3mf it's all guesswork.
Formerly known on this forum as @fuchsr -- until all hell broke loose with the forum software...
RE: Print issue only when setting Infill to Lightning ... Bug or not Bug ?
OK, Thanks ! I'll increase infill from 5 to 20% and select Gyroid instead of Lightning.
I attached the 3mf file of course, but it seems it has been dropped somewhere 🙄