Thanks for the hint! I set up cron job which pings www.google.com every minute (cron tab). The system log reports the ping every minute. Unfortunately this doesn‘t solve the issue. Obviously the ping traffic is not enough.
Do you have a hint what else I could try?
Did it like this: */1 * * * * ping -i 5 -c 60 www.google.com
Can you set the interval smaller?
Another test is to use wget or curl to download Google website
Still don‘t get the disconnects fixed 
Any help and idea is highly appreciated!
I have just started facing this issue. I am using latest iphone with latest ios tethered to MT300N V2 router. The tethering connects but fails to provide internet access on the clients. Looks like some issue on Gl.Inet router side. When I connect iphone directly to my pc the internet works fine no issue at all. I tried resetting the router and iphone but the issue still persists. plz help.