The issue is with the PPPoE authentication process and that might be caused by something on the ISP's back-end.
The ppp instance on the router is issuing a SIGTERM (for unknown reason) signal
If you want to try to debug the matter it would require to alter /etc/ppp/options and add
debug
kdebug 7
also try with the ppp options (same file)
passive
maxfail 0
persist
The final process arguments pppd is running with can be queried with ps -aux | grep pppd - 
you may want to obfuscate potentially private data such as username | password
For verbose debug output in the logs of netifd it would require to edit /etc/init.d/network
modify procd_set_param command /sbin/netifd by adding -l 5, it should read then
procd_set_param command /sbin/netifd -l 5
and add below that line
procd_set_param stderr 1
Once done/set execute service network restart ; logread -f