"Timeout waiting for PADO packets" until reboot

Hello

My parents have an FTTH connection with an Asus DSL-AC68U router which
runs linux and pppd version 2.4.7. The network devices are connected
to a UPS for stable power.

Options configured:
lcp-echo-interval 10
lcp-echo-failure 15
lcp-echo-adaptive

If there is a short, let's say only 10 minutes, outage between the
home and the ISP, the router prints
"pppd[17084]: Timeout waiting for PADO packets"
messages but it is able to re-establish the connection automatically
when the outage is resolved.

However if the outage is relatively longer the router just keeps printing
"pppd[17084]: Timeout waiting for PADO packets"
messages and even if the outage has been resolved the router is not
able to re-establish the PPPoE connection. However after a reboot the
router is able to establish the PPPoE connection without problem.

Because I am remote I am not able to access the router for
troubleshooting during outage.

Others have the same problem for example with OpenWrt where I also see
ppp version 2.4.7 is used
https://github.com/openwrt/openwrt/issues/7826


Would you please help what can be the issue and how to fix it?

Thank you!
Best regards
David