I've been getting the same error message intermittently for at least 4 months and probably a lot longer.
Blue Iris is running in a Windows 10 VM that is blocked from the internet. Randomly Blue Iris uses 100% CPU for a long time, maybe 2 - 3 minutes and occasionally longer, which locks the pc up. It will usually start off by spiking to 100% for 30 seconds or so, and then going back to the normal 10% or so for a while, before spiking to 100% again. It can do this repeated spiking for hours, or only minutes, before it stays at 100% for multiple minutes and locks the pc up.
I've checked the Windows and Blue Iris logs and cannot see any entries that help fault find it. Rebooting the host pc and the Blue Iris VM is the only way to stop it until the next time it starts doing it. Just rebooting the Blue Iris VM doesn't stop it. After rebooting both it can then be ok for a day, days or even weeks, before it will do it again. Deleting Alerts or Clips does seem to initiate it, but not always, and not always immediately, and sometimes it will do it if nothing has been deleted.
The fact I have to reboot the host pc, which is running Linux Mint with an I7-8700 CPU and 64Gb ram, seems to imply that it's the VM program getting upset in some way by something Blue Iris is doing. I've learnt to live with it. It's annoying when it happens but fault finding it is too time consuming. I'm hoping either a VM program or a Blue Iris program update will cure it.