Gzip: stdout: No space left on device

I’ve been getting this error message for the past few days:

cron for user root /usr/bin/run-parts /etc/cron.daily 1> /dev/null

error: Compressing program wrote following message to stderr when compressing log /var/log/nginx/error.log.1:

gzip: stdout: No space left on device
error: failed to compress log /var/log/nginx/error.log.1

However, I can’t figure out what’s causing the error, since there’s still enough free memory available:

df -h
Filesystem                         Size  Used Avail Use% Mounted on
tmpfs                              794M  1,2M  793M   1% /run
/dev/mapper/ubuntu--vg-ubuntu--lv  154G   25G  123G  17% /
tmpfs                              3,9G     0  3,9G   0% /dev/shm
tmpfs                              5,0M     0  5,0M   0% /run/lock
/dev/vda2                          2,0G  260M  1,6G  15% /boot
/dev/vda1                          1,1G  6,1M  1,1G   1% /boot/efi
tmpfs                              794M  4,0K  794M   1% /run/user/1000

What can I do here?

I’m running the current version V76.