No model file to check, no factory file... so I'll have a guess based on the pictures:
Missing walls etc. can be caused by broken model files/errors within the model.
But looking at the perimeters I wonder if settings regarding coasting/wiping are causing this?
Missing walls usually don't result in things like the outer but not the inner perimeter
showing up in the sliced result. Things might be different with v5 and its different repair
algorithms, though. Not using v5, can't say much about that. Did you test the various modes
and if they make a difference?
Blue perimeters on the back in the pictures aren't deep blue as the single extrusions on the "X",
so I'd check for coasting/wipe etc. first.
Edit: Extreme coasting/wiping creates results not so far off, depending on start point location. I'd
recommend adding a factory file so others using v5 are able to have a look at the settings.