Connected to TeamViewer Host but cannot see remote screen


Thank you for this free app. It's great for helping my mom who is new to smartphones. I could control her phone remotely for a couple of months but since yesterday, even though it's connected, it doesn't show the remote screen. When I tried connecting again, the following message is shown

"There is already an active connection to this device. Multiple remote control connections to this device are not possible"

There is no button to disconnect and all I could do is restart the app on my side. It doesn't help though. What can I do?

Thanks in advance