Thanks for the reply. I tried amending the manifest.json then creating a shortcut but unfortunately that didn't work. Looks like you're right regarding Chrome, I've just installed the Chrome Beta release and it's working again, looks like they broke something. To get it working in the Beta I had to remove the "start_url": "../ui3.htm" line from the manifest and this way it stored the page I had open in the browser (including arguments) as the start page when I click "Add to Home Screen", otherwise it just opened the standard UI3 home page.I have no idea what changed. It wouldn't have been a UI3 or Blue Iris change most likely, so my guess it is something in Chrome. I believe they did recently release an update related to "progressive web applications" which probably would have touched this feature.
As a workaround, you may be able to find the "manifest.json" file in your ui3 directory and edit its start_url parameter to include the arguments you want. Then save a shortcut to your Android desktop. Then change the start_url again. I can't guarantee your shortcuts will retain the change afterward since I have no idea how it works under-the-hood, but it is worth a shot.
It is in the "PTZ Controls" section. Yours are hidden. You need to show them by right-clicking somewhere in the cameras area and choosing "Show PTZ controls". I believe the Blue Iris window also has a minimum size to show the PTZ controls, so at very narrow sizes they won't appear.