I have been having PPP drops on my Asus RT-AC68U so I converted it to a wifi AP and turned my ZyXel VMG-1312-B10A into a router which was being used as a bridge modem. I have 3 Zyxels and earlier in the year PPP was dropping so I swapped out the modems and it stopped. But recently it started happening again so I reconfigured the Zyxel as a router but it dropped at 8.34 this morning. I have a script to download a 1gb at 32 minutes past the hour every hour and the ZyXel was fine up til 8.34 this morning. It usually gets to about 800mb downloaded and then the PPP drops and its very random.
I have swapped the Zyxel with a 3rd 1312 and it has been fine all today, further testing needed. I have been talking to my ISP and they want to send an engineer but I doubt they will have the skills to diagnose this type of fault as it only drops when under load. Could it be I am not powering off the Zyxel often enough?