Server falling asleep and mysterious syslog entries

Question

I am running Ubuntu server 16.04 on an old laptop. I have had consistent problems for several months with it falling asleep: it will drop its network connection (I am not using wifi) and from the lack of fan noise, I can tell it also stops working on the distributed computing projects I have it do. Up until a few days ago it would go up to ten days or so without falling asleep, but now it is almost every day. Previously, I wrote a cron job to ping Google regularly to keep the computer awake, but it does not seem to have helped. Below is a recent syslog entry. The 8:44 events are me manually restarting the laptop. Why do the entries just stop? What does the

@^@^@^@

mean?

I do not believe my problems are due to, say, closing the lid, as I have set systemd to ignore that. Here is a log excerpt:

Nov 30 12:33:01 MouseHouse CRON[3047]: (root) CMD (ping -c 5-n 8.8.8.8 )
Nov 30 12:33:05 MouseHouse CRON[3046]: (CRON) info (No MTA installed,   discarding output)
Nov 30 12:34:01 MouseHouse CRON[3051]: (root) CMD (ping -c 5-n 8.8.8.8 )
Nov 30 12:34:05 MouseHouse CRON[3050]: (CRON) info (No MTA installed, discarding output)
Nov 30 12:34:17 MouseHouse kernel: [14051.835340] [UFW BLOCK] IN=enp2s0f0   OUT= MAC=01:00:5e:00:00:01:a0:63:91:04:52:68:08:00 SRC=0.0.0.0 DST=224.0.0.1 LEN=32 TOS=0x00 PREC=0xC0 TTL=1 ID=0 DF PROTO=2 
Nov 30 12:35:01 MouseHouse CRON[3054]: (root) CMD (ping -c 5-n 8.8.8.8 )
Nov 30 12:35:05 MouseHouse CRON[3053]: (CRON) info (No MTA installed, discarding output)
Nov 30 12:36:01 MouseHouse CRON[3057]: (root) CMD (ping -c 5-n 8.8.8.8 )
Nov 30 12:36:05 MouseHouse CRON[3056]: (CRON) info (No MTA installed, discarding output)
Nov 30 12:36:23 MouseHouse kernel: [14177.266465] [UFW BLOCK] IN=enp2s0f0 OUT= MAC=01:00:5e:00:00:01:a0:63:91:04:52:68:08:00 SRC=0.0.0.0 DST=224.0.0.1 LEN=32 TOS=0x00 PREC=0xC0 TTL=1 ID=0 DF PROTO=2 
Nov 30 12:37:01 MouseHouse CRON[3060]: (root) CMD (ping -c 5-n 8.8.8.8 )
Nov 30 12:37:05 MouseHouse CRON[3059]: (CRON) info (No MTA installed, discarding output)
 ^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@
 ^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@
^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@
Dec  1 08:44:50 MouseHouse rsyslogd: [origin software="rsyslogd" swVersion="8.16.0" x-pid="1192" x-info="http://www.rsyslog.com"] start
Dec  1 08:44:50 MouseHouse systemd-modules-load[422]: Inserted module 'iscsi_tcp'
Dec  1 08:44:50 MouseHouse loadkeys[439]: Loading /etc/console-setup/cached.kmap.gz