Since I updated to High Sierra the Preview app no longer remembers the sizes and positions of its open windows. Instead it just opens all windows on the same desktop with standardised size and position when the computer starts up.
How do I fix this?
(Side note: After updating the Preview app also didn't remember the last viewed page of PDF-files, but I was able to fix this by deleting the
~/Library/Containers/com.apple.Preview folder. However, the window size and position issue persists.)