Teamviewer for Android not working or lagging?

Question

Android

Dear colleagues!
Please advise about Teamviewer.
There is:
Beloved 80-year-old granny who has an Android phone [ Samsung SM-J320F ] with all the consequences...
Internet access via 4G [MTS - moscow]
Teamviewer for Android + Plugin for Samsung(Teamviewer) is installed on the phone
Access is via Email , password.
You need the ability to always have access to her desktop on the phone to correct all sorts of situations due to "crooked hands".
Teamviewer is often naughty, namely, it turns off at the moment when something happens and it needs to be fixed.
Now teamviewer is running in eco mode on Android, while logged in and has access to the network, but there is no way to connect to it.
Example:

What could be the reason for this behavior?
[reboot does not help;)]
It often happens that everything goes wrong on the phone, namely Whatsapp asks to re-verify. Happens every 3-4 months.
It's like there are no viruses. No links are clicked.
Has anyone experienced this type of behavior and what should you do in this situation?
Maybe there is some more advanced program other than teamviewer that will not let you down like that?
I would be grateful for any advice and just thinking out loud!