About disconnecting wwan0

Hi
I upgraded the kernel version of the BBB board to 5.15 and the debain version to 11.5.
And BBB is connected to LTE Modem using usb.
I succeeded in getting the ip address from the lte modem through the following command.

sudo /sbin/dhclient -v wwan0

After a successful connection, I ran a ping test with the command below,

sudo ping 8.8.8.8

but after about 2 hours, the network through the LTE modem was disconnected.
So when i check with ifconfig, no IP is found in wwan0.

If I run this command again, ‘sudo /sbin/dhclient -v wwan0’, the IP will appear in wwan0 normally,
and ping will also be connected normally.
Below is what I tested.

The files in the following path are the same for kernel 4.19 and 5.15
I don’t know why the connection doesn’t drop in 4.19, but it drops in 5.15.

 /etc/dhcp/dhclient.conf

I don’t know why the network through let modem is disconnected after about 2 hour.
Can you tell me the cause and how to fix it?

Regards,

This is why we don’t force kernel upgrades by default, just downgrade to your previous 4.19 based kernel…

Regards,