I have a Tronxy P802E, which works pretty well for me. I currently use Ultimaker Cura 4.1.0. However, I occasionally get a weird problem where the walls in certain parts of certain prints will be highly porous.
Contrast the following similar, yet non-porous, structure elsewhere in the print:
(Note, though, that you can see porosity in the wall of the triangular structure on the right.)
I've printed this twice - once with retraction enabled, and once with retraction disabled. Porosity occurred to the same degree, and in the same places. It's neither a jam nor general underextrusion, because it occurred on every z-layer in the same set of xy places, but not in other xy places. It makes me wonder if there's something about the order that Ultimaker Cura codes the structures to be printed in, that causes this problem - like if it's e.g. transitioning from one wall to an opposing wall after infill, triggers low extrusion, or something like that. I further wonder if it's a problem in gcode or something that occurs in the physical act of printing. Has anybody seen this before? Have they solved it?
Oh, this may or may not be unrelated, but when I've watched the infill, I notice that there's frequently little gaps just before or after crossing another infill line. I may make a separate question about that, eventually, if it's not related to this.