Ping not responding every 5 minutes on Ubuntu desktop 18.04.1 LTS

Question

I set up a Ubuntu server by Ubuntu desktop 18.04.1 LTS + apache2 + PPPoE. I find that I got disconnected frequently. I ping the server and the requests are timeout for about 30 seconds every 5 minutes. And I think it is not the apache issue since this issue is still reproduced after I stop apache. I also set the "automatic suspend" to off and "blank screen" to never in Settings->Power but I still encounter this issue.

I try to connect the network cable to another Windows 10 laptop and ping the laptop, I don't encounter this issue on the laptop.

Which Ubuntu settings would cause this issue?

Ping status:

08:40:20 Succeeded
08:40:23 Succeeded
08:40:27 Request Timeout
08:40:31 Request Timeout
08:40:35 Request Timeout
08:40:39 Request Timeout
08:40:43 Request Timeout
08:40:47 Request Timeout
08:40:51 Request Timeout
08:40:55 Request Timeout
08:40:59 Succeeded
08:41:02 Succeeded
08:41:05 Succeeded
...

08:45:41 Succeeded
08:45:44 Request Timeout
08:45:48 Request Timeout
08:45:52 Request Timeout
08:45:56 Request Timeout
08:46:00 Request Timeout
08:46:04 Request Timeout
08:46:08 Request Timeout
08:46:12 Request Timeout
08:46:16 Succeeded
08:46:19 Succeeded
...

08:50:56 Succeeded
08:50:59 Succeeded
08:51:02 Request Timeout
08:51:06 Request Timeout
08:51:10 Request Timeout
08:51:14 Request Timeout
08:51:18 Request Timeout
08:51:22 Request Timeout
08:51:26 Request Timeout
08:51:30 Request Timeout
08:51:34 Succeeded
08:51:37 Succeeded

Thanks