User losing access



I've assigned access for a guest user to 10 sheets. She can activate it & use it without problems for days at a time.

Then one morning she doesn't have access anymore to 1-2 sheets. Nothing changed though on both her or my side.

Only way to get her access back is to delete her as a guest user & re-invite her. Only to be told a a couple of days or weeks later that it's not working again.

I've got many guest users & she's the only one struggling like this in my 6 years of using SmartSheet.

Please advise as it gets very irritating have to re-invite her every time?