Your
Blue Iris machine may not have enough free resources for smooth playback on that camera. Or the stream from the camera's hardware is weak and glitchy. Or network hardware is slow somewhere.
I've seen that before on my earlier BI boxes.
One time I solved it by using 2 Hard drives and splitting the writes and reads across 2 disks,
to try and unchoke any bottlenecks associated with Spinning drives.
This resulted in a big improvement on my hardware back then, I think it was an i7-3770s FrankenDell 7010.
So now I run 2 WD PURZ drives.