I create a file in Adobe Illustrator 1500px wide by 1000 px tall. I export it as a layered PSD and when I open it in photoshop it's only 400px wide and it's not proportional, the strokes are all really wide compared to the rest of the design. Sometimes it exports fine, sometimes it doesn't and I'm not doing anything different??
Illustrator does not use pixels as a dimension, Yes, I know it says it does. This is wrong. Illustrator uses points as pixels, assuming that the artwork will be exported or saved at 72 ppi (pixels per inch) which is basically the same as one pixel of image data to one pixel of screen display.
If you export at 72 pixels per inch, then each of Illustrator’s points (wrongly called pixels) will be saved as a pixel in the Photoshop file.