There is often no rhyme or reason with dementia and changing behaviors, once the obvious causes of pain and hunger are ruled out. I would suggest the person visiting daily to cut back on the visits to twice weekly for just an hour and to do something while there. Being expected to chat or to answer questions can be infuriating, especially if the person has decided they are angry with the visitor. I find movement works well- pushing the person around the facility, pointing out this and that (lots of holiday decorations now), going outside to the patio or walkway if the weather is good.
It’s important to respect the person’s moods, if they’re angry- say, “Good-bye for now, see you soon”, and leave. It will be hard not to feel rejected and sad, but the disease is messing with their mind, it’s not you.