I am having the same issue on a Linux based system, version 8.1.We use a shared database and I can tell you the the same issue occurs when I open the project on another resolve. As above I am monitoring in SD and find I need to resize the project to be able to see a correct image on my SD broadcast monitor. It seems to me like Resolve is not designed to switch between project size in this way, however I have found no other way to monitor a HD project in SD with my workflow.