What does this mean in Blocks?

Working on a project with multiple blocks. I’ve had this icon appear before, but never understood how I got in and why it changed. Is there an explanation?


Hello - are all the parts you expect to be in the block there if you explodeBlock?


I’m not sure. I moved on but saved the image when it appeared a couple weeks ago and wanted to ask the question. My model had many blocks and at some point the block label turned into that icon. I assumed I did something, and wondered if it was a common error?