P9 Lite

I link teamviewer from OnePlus 3T - with Nougat - to the P9 Lite - with Nougat too - (my father's smartphone who is 84 years old) and until recently it worked but lately on my phone appears this message:

"The interlocutor did not confirm the request of his own screen. The connection was then interrupted."

But it's not true, I tried it myself tens of times and with the Samsung Note 2 (of my 80 year old mother) it works regularly. So I tried to clear the data, the cache and uninstall the app and then reinstall it but the problem persists. What can I try to do?

Thanks so much. Beppe

p.s.
I write from Italy, sorry for my bad English