Have got a very bizarre error now showing up on two projects within 3 weeks on different machines. No shared assets between them.
A red wireframe has appeared on one of the layers and won't disappear from its position in the timeline, no matter how many times I recreate an edit, or reposition clips. If the original media is there, the red wireframe is there.
Trying that method now, though I was able to recreate it on another machine by simply having layers involving some sort of alpha channel. Specifically it was a picture background, with another photo on top. No third-party plug-ins, but still have the red X.