Indoor Camera viewable on my phone but not my partners

We’ve had the indoor camera for around a year and the app has worked fine to view the indoor camera on both mine and my partners phone. Recently this changed and now they can only view the camera when they’re on mobile data on not our home WiFi which the camera is also connected too. But she can still view the house doorbell no matter what internet source she’s connected to.
We have reset the device, reconnected it to the WiFi, redownloaded the app, reconnected the phone to the WiFi and restarted the phone but nothing seems to have helped.
Any advice would be much appreciated.

Does she use an ESim? Many similar issues have been reported by users of Esims. Usually switching to normal Sim or using a particular VPN app will solve it. There have been many posts of this issue here and on Reddit.

Thank you for the reply but she just has a standard physical sim no eSIM.