OK, I'll add something to a month old thread to maybe help someone..... I was having the same issue. Yellow exclamation point. I looked at the help file, searched here. Found lots of answers regarding mismatched frame rates at the camera settings and
Blue Iris. I double checked every setting, checked BI for updates, deleted and reinstalled the new camera (new Dahua, replaced an sv3c). System running at 18% with 5 cameras, plenty of RAM.
The boggling issue is that the exclamation point kept switching from camera to camera. Cameras that I knew were working fine a couple of days ago and none of the settings had been changed.
So how did I fix it??? I finally decided to reboot the PC that's hosting Blue Iris. As it turned out, the PC had updates pending and took a while to reboot. After the Windows updates and reboot, all of the issues were gone.
Moral of the story, sometimes "Explained in BI help file" isn't enough", specially for those still crawling through the sometimes steep learning curve of our hobby/job/passion.
All of the checks and re-checks of settings could have been eliminated if only I had rebooted the %*!@#$%& computer first!