Yes, I looked at the pictures. We tried to reproduce the issue with the model and settings you linked to but were unable to.

In its current implementation, Expand Thin Walls is really meant more for touching up small areas within a print that would otherwise not render properly without the setting enabled. It's not intended to be used to expand an entire perimeter like the box you're trying to print. The walls are 0.5mm, which is exactly the nozzle diameter, and this makes operations difficult for the slicer. Increasing the walls even to 0.51 would be much easier for MatterSlice to work with. I will make a note about the issue you're having with the functionality of this setting, but I don't expect any quick changes to the way it works so you'll probably want to modify the model instead.

MatterSlice's thin wall support is a work in progress. In the mean time, what you can do is increase your nozzle diameter setting until the perimeters meet in the center, so that no infill is needed. We have actually had a lot of luck with specifying a nozzle diameter slightly larger than the actual size.

thanks, that works better then making the shell 1 mm thick... never had that issue with Slic3r, but, so far i am liking MatterSlicer - the bed leveling works... i was having a nightmare with Repeiter firmware getting it to map the bed. Got a Zprobe, but, could never get it just right. I used the 7 point, then the 13 point on MatterControl, and i can lay down a flat 1st layer all round. My Rostock Max is 2 1/2 years old, and now that i have updated the arms, got an all metal E3D head, and now switched to MatterControl, it is working better then it ever did - like i got a whole brand new printer

Yea messaged the creator and he made the lines thicker so I only had to scale up the model by 10% which is no biggie. I got it to slice correctly after he made the lines thicker but I still have another problem when printing the outer ring gets dislodged while printing and messing up the whole print so I was thinking of adding some support to the outer ring to connect to his manual support so it wont dislodge. I have my fan on max but the plastic still curls like crazy so I will try adding some support so the outer ring doenst come off while printing.

This is the toughest thing i've tried to print and I have printing a lot of stuff this is the first thing giving me trouble.

Thank you for your help.