You probably don’t have a swap partition, go to system settings misc and enable the 2GB swap file option and reboot.We added this specifically for such systems, it seemed to solve such issues. But the setup is manual.
/usr/local/bin/python2.7 /usr/local/opnsense/service/configd_ctl.py interface newipv6 ppp
Is there a hardware spec for your device somewhere to skim through?