Looking at the MTL-file with a text editor, I noticed that the medwood-JPG file isn't mentioned. Is that file not needed, or is it omitted for some reason?

I'm not really sure how it works to be honest, but it's nothing I've done. I just want whatever ends up being imported to SH3D to have more than one editable colour/texture as I like to change them within the homes rather than predict the colour in general. In this case, the main design feature that made this model interesting was the concept of having coloured shelves, which is why it was such a blow that there was a possibility the solution was going to need to be a blank model.

Microsoft/Windows or the 3D printing goal might be where the issue is coming from, but whatever the issue is wasn't happening before this model and hasn't happened since (I think I made one thing since and imported it no issue, no more than that yet.)

I really do use 3D builder just because it's there on my laptop to be honest XD I don't have the experience on other 3D modellers to know if I'd be able to use them or not, 3D builder more corresponds to lego or model planes, putting different shapes together and painting them, it's not high tech, at least not in my hands. XD

Then I did a couple of tests with 3D builder. Just boxes and cylinders with and without textures. The exported .obj/.mtl/.jpg imported as expected in SH3D. Which means I do not understand what has happened with your .obj file.

But I took the liberty of messing a bit with the parts of your file I managed to export, simplifying a bit. Round legs in 3D Builder are very detailed, possibly useful for 3D printing, but not needed for SH3D. Even by Cec standards. Then I added texture mapping all elements (say if you want the same wood in one or more of the shelves). But as this was a quick and dirty test, I may have ruined your original proportions. Not too much I hope.

I really don't get why it's doing it either, but I'm really grateful for your version of it! The original proportions were never very important to me but even so I can't really see how much they've been changed. I'm just really happy to have something that looks like what I intended in my model at last Also the number of faces on the 3D builder cylinders and how complicated they can be to paint unless you're going for a block colour bugs me too XD They really don't need so much detail for a rounded edge. I can only assume it's down to the 3D printing thing also.

Thanks again!

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With SH3D finally accepting this variant of the model, my problem is now solved until/unless 3D builder does it again. I am still interested in what caused the problem, so I may be able to fix it in future, if anybody has any future input, but we need not spend any more time guessing at answers that we can't figure out until a more solid answer comes along (unless you want to of course ). Thanks all for your time