I think I have the same problem, or even worse, PPPoE stuck at random times after power on from few hours to 30 days, has to be rebooted manually, also the router reboots itself randomly.
I have two ac68u, one r7000, two ac86u and one ax86u, all of them are running merlinwrt 386.3_2 now.
I start noticing this PPPoE issues from about 2 years ago, my family members started complaining about they couldn't access the internet, and had to reboot the router. I think all this starting from 384.x, before that ac68u and r7000 have never needed to be rebooted even after a year.
I have an online notification script, and I have found a strange behavior recently, my router online notification can be as later as up to 10+ minutes sometimes after reboot, it normally should be less than 1-minutes.
Today my network went down for several hours again and I logged into my ax86u, to check what was going on with my router. And there was nothing/empty/totally blank in the log, I saw this phenomenon once before when my internet went down, I thought it was a coincident, so I clicked the "Clear" button, then the new log was showing up. And this time all the same, when I clicked the "Clear" I saw `pppd[1931]: Timeout waiting for PADO packets`
And even more strange was, since my internet went down I had to switch to a backup router, so I changed ax68u from PPPoE to Dynamic IP, and plugged ax86u to my backup-router, but the ax86u kept showing me its Internet status disconnected, I rebooted ax68u again, it was still showing disconnected, even I could ping my up-link router IP address within SSH, and the log shown `pppd[1931]: Timeout waiting for PADO packets` , but the router was set to Dynamic IP mode, which made me wonder something was wrong.
So I have tried to manually set back and forth to PPPoE and Dynamic IP, but not working, I still got Internet status showing disconnected, then I switched to Static IP and the Internet status showing connected, that was very weird.
Those ac68u ac86u ax86u and r7000 are running under several different ISPs, all of them more or less had random reboot and PPPoE stuck issues lately, it is getting even worse since 386.3_2.
I have 4 houses with 4 different ISPs and locate in two counties.
ISP A is PPPoE and IPv6 native capable and IPv6 is switched off. With ac68u, random reboot, PPPoE stuck, problem started from latter half of 2019, after update to 384.13 probably.
ISP B is PPPoE and IPv6 native capable and IPv6 native is switched on. With PPPoE stuck started from earily of 2019, after update to 384.x not sure. Now with 386.3_2 ax86u, ac86u, r7000 random reboot + PPPoE stuck + needs 10-minutes to get online sometimes.
ISP C is PPPoe and IPoE capable and IPv6 pass-through is switched on. With 386.2_3 ac86u ac68u, most of time is stable, occasionally failed PPPoE.
ISP D is IPv4 only and Dynamic IP. With 386.2_3 ac86u, random reboot.