On one of my computers sony .arw do not show a preview in Bridge (in every bridge; 2015, 2017, 2018). The problem might be a corrupt preference in Bridge. However Bridge on my other computer handles .arw files well. They both are running os x high sierra and Bridge 2018. As I have made several custom standard preferences for specific camera number and specific iso, I like to copy the preferences from the bridge version that works well to the computer that doesn't work well with the .arw files.