Oh yes now I know.
This issue appeared after the last app update
Before you could view 4 cameras all at once , now in landscape mode it’s switched to vertical format and you only get 2 camera live feeds and their cut in half.
It’s not only on iPhone SE and 8, I think it’s newer models as well.
This was mentioned a while back, you can check out the discussion here Grouped cameras grid view in lanscape mode
I am using an iPhone 8, running the 2.40.0(15) app and I’m experiencing this issue.
Here’s a log in case you need it.
1005746