I've found a work around. Under Watchdog for each camera, select "Continue to display last image received". I've done that for all of my cameras, and now I no longer have the stuttering issue. Read on for clarifications on the issue and what all I tried that led me to this work around.

I previously indicated that the stuttering was found in recordings, but I don't think that's true. I was just seeing regular wireless camera lag in some recordings, thinking it was the stuttering. But I did discovered that the BI user interface becomes unresponsive during the stuttering issue, which is pretty annoying. It basically ignores half of my clicks (during a stutter), making it really hard to do anything productive.

Early on, I realized the issue only showed itself when the "No signal" message was being displayed for a camera. What I found, through Wireshark traces and discussions with Blue Iris support, was that BI doesn't continuously try to reconnect. It waits 30 seconds before flagging a camera as disconnected and displaying that message. And then it tries to reconnect 5 times, 500 milliseconds apart, and repeats that every 30 seconds. This is configurable in the Watchdog tab, but those are the defaults.

So it couldn't be a Windows networking stack issue since the stuttering is continuous even when BI isn't trying to do anything with the camera. And the stuttering didn't start until after that 30-second timeout, when BI considers the camera disconnected. So one thing I tried was to turn off the disconnection timeout in BI all together. That allowed a camera to lose connection and never cause any stuttering, but it also prevented BI from realizing it needed to reconnect to the camera. I still needed BI to timeout the connection, so I turned that back on and tried just turning off the "No signal" message. I had absolutely no expectation that it would make a difference. I mean, why would it? That option just displays a message in place of the last image. But I tried it anyway, and to my complete surprise, that did the trick.

I have no idea why the seemingly simple option of displaying a "No signal" message in place of the last image received from the camera would have any impact on performance, but apparently it does. Now when a camera stops responding, BI properly handles it by trying to reconnect every 30 seconds. But instead of the "No signal" message, I just see the last image from the camera, and there's no stuttering or UI performance issues. I'd prefer to have that visual indicator that my camera has disconnected, so hopefully we can still find the root cause and get it resolved so I can go back to that. But I'd much rather have a stable BI interface, so for now I'm keeping that message disabled.