Thanks. Please post a more complete log. Some process has died, causing some other process to fail to write to it.
It’s a good idea also to look in the kernel logs for out of memory conditions
dmesg | egrep -i "memory|oom"
and if you find any please post the surrounding context
dmesg | egrep -i9 "memory|oom"
As you have lots of free disk space, adding more swap may help. You should also be sure you’ve made the kernel settings changes as recommended in MKJ’s Opinionated Discourse Deployment Configuration