If nothing is showing up in the logs, then the triangle in the top corner of the camera border means it is an issue with the stream whether it is apparent or not.
Many of us have seen this happen with recent updates. Update and get this or another issue like notifications don't work and rollback and they work again.
Even though the image looks fine, it is causing an error in the BI camera - it could be it is having trouble processing both streams, trouble with HA, etc. It may go away after a minute or it may not. Hit the find/inspect on the camera and see if that gets it going.
But you also don't have to run the latest version either. If yours works as intended in .11, I do not think anything was added between .11 and .18 to live on the bleeding edge. Many of us run an older version that is stable and only update when something we need or want is added.