I just downloaded 2.8 after a long hiatus from Blender. It was going so well learing the new interface but them the knife tool started acting up. I tried appending the model into a new file but is still doesn’t want to work with this mech.
Same here, the Knife tool is not new at doing strange stuff, and in this case doesn’t seem to be snapping to the polygons in front, but only to the one in the back, even if you scale up the model, which looks small, but that’s not the problem.
I also found that the knife tool never was as reliable as in e.g. 3DSMAX.
Sometimes it works as expected, just to fail on other parts, give strange erratic geometry and require manual fixing.