Wondering if anyone can help?

Mrs Tek's mobile is playing up badly.

It's a Samsung S6 and the screens she are on keep jumping about.So for instance if she was on Tekel Towers it would keep minimising the screen them maximising it...jumping off the app...going onto another one etc etc.

She isn't due an upgrade for a year and it's just too expensive to replace.

Anyond had similiar issues or have the foggiest idea how to solve this?

Thanks in advance.