Transparency issues when exporting

I think I've hit a possible cause for the bug.

Can't reproduce it though (scarce on time at the moment), and I haven't yet figured out how to make it misbehave consistently (unfortunately, that's what bugs are allowed to...)

But as I was looking at your design and editing description, I noticed that in order to keep the blue element appear within the transparant box, you rightfully needed them to be grouped, otherwise the receding part of the blue box can't be overlapped by the transparant red, while keeping its frontmost line black. But as I was testing some non-grouped elements (as well with transparencies), everything exports okay !

So it's not a total incapacity of the PNG or JPEG algorithms to deal with transparency in objects with 3D effects. It must have something to do with the grouping, that triggers this odd behaviour...

I have this same issue, it's very frustrating! The sketch looks great in Illustrator, I have many opaque boxes extruded within a layer of layer of 15% opacity of the same thickness, but when it comes to exporting to PNG, no matter what settings are applied, the layer comes out as one opaque block... not at all the design I'm going for. I'm working on a windows machine if that helps. I will likely have to result to the result Chad Chelius recommended, sadly...

Try this

1. Select your 3d object

2. Go to File, Export selection

3. Click on the little gear and under the background color choose Transparent and save settings

4 Export asset

5. Done, your file must be transparent

Does it have to be transparent in the png, or just keep the effect of looking transparent?  What if you draw a solid white background behind your object?  Then it would maybe export solid, but appear the way you want?

Would normally suggest expand appearance or rasterize, but that does nto work here. 3D extrude is  buggy in Illustrator.

Since you like what is on screen, zooming in and taking a screenshot, might be an option? Or expand appearance to get the shapes and recolor them to what you need top also get the transparency if needed. While my suggestions might be the solution you  you are looking for, they might be your best options.

It seems that with the settings you've used, Illustrator is unable to replicate what it's producing. I've tried making a pdf, placing into InDesign, exporting to .psd, and each time it can't replicate what it's showing in Illustrator. I know it's using transparency settings to achieve what we're seeing, but it's having trouble rendering it out. Short term, my best solution since your trying to export to .png, would be to just take a screen shot of it. It's definitely very strange that it can't maintain what we're seeing.

Do you use the overprint preview in Illustrator?

Is the outher shape set to multiply?