Hi Neil and welcome to the community I hope one of us can help you.
You posted some hours ago and no one has picked up on your problem so far. Now I am not a Roon user so I cannot help with anything specific related to that. However on a general note we do get quite a few posts about odd things happening where the simple solution is to re-set the device. I am not saying that this will be the answer in your case but it should be tried and you haven’t mentioned it. Simply switch Network Bridge off from the rear panel, wait a minute or two and switch it back on.
If it isn’t successful then you will need to wait for a response from someone with Roon expertise. It may help them if you would advise them of the version of Roon that you are running as I understand that there have been a couple of updates over the past year or so.
Neill, on community.roonlabs.com there are almost daily reports of Roon Remote crashing on smart phones. The most likely culprit of your recent troubles is either iOS updates or Roon updates. I doubt changing anything on the dCS Network Bridge is going to help.