Fullscreen 1 is showing output only, will not show/select any other sources. This is new behavior. Tried changing the source both from dropdown and by script, no luck. Using a laptop (MSI GT73 VR)with a nVidia 1080 card. The two fullscreens are fed by a mini display port and a hdmi port and both displays work fine, even when switched in either the Windows(10) display settings or the nVidia settings. And I have verified in vMix settings that the Fullscreens are attached to the right displays and are sending video. Fullscreen 1 just seems to be stuck on 'Output'. Any ideas?

FWIW, I have TB3 attached to a decklink duo2 card and all that video is just fine as well.

Edit:Just tried this with a new project and both Fullscreen 1 & 2 behave normally, i.e. both allowing me to change sources. But back to the other project with all 4 Outputs as well as both Fullscreens being used and Fullscreen 1 remains on 'Output'only.

Ice Stream, thanks. That makes total 'vMix' sense. And yes, Output 1 was set to output an multilayered input... I was recreating a live show I had done with an Ascender(a 4 output screen switcher) as a vMix project and had for various reasons set it differently than I might otherwise have done. Thanks again.