We have a team of 4 developers working on an application (using Co-Authoring), when three developers reported to me they were no longer able to view the application correctly. I continued developing for some hours, and then refreshed the page. Same thing occurs for me. I connected the Live Monitor to the studio session, nothing registers in play mode. The developers were able to create new screens and develop on them, however the controls on those screens also don't show up in the live monitor. I've change the authoring version to the latest (one step forward from the version I started with) and two versions back, with no change. I've set the display ratio to scale, and then back to dynamic, still no controls register, all previously created screens are wildly distorted and non-functional.
As I was writing this out, I tried turning Co-Authoring back on (I disabled it earlier, which fixed nothing). As soon as Co-Authoring was re-enabled, everything started working again. So if anyone has this happen, that's what fixed it for us.
I'm off to go have a mild heart attack now.