Export a frame of 375W to 2.4x and get 901px

This is where the frame locates. I thought negative positions were not sub-pixel.

True, but there is a catch. They aren’t sub-pixel in 1:1 export but they can be in different size exports. Let’s say you are exporting a node in 1.5 for example. Technically, the whole canvas would be enlarged to 1.5 to export this piece at this resolution. This would result in fractional numbers in coordinates. If your frame is standing on coordinates (3, 11), then the result will be at coordinates (4.5, 16.5). I don’t know why it works this way but it does. So to ensure your export at 2.4x works correctly, the object needs to be standing on coordinates divisible by 5 (because 0.4 is 2/5). Alternatively you can set the export dimensions explicitly (e.g. 900w as 375*2.4=900), this way the canvas shouldn’t multiply this way and the coordinates can be any integers.