PPPOE issues: KPN FTTH with Linkysys WRT1200AC V2 & latest OpenWrt 21

I have configured the vlan6 on WAN as device and created an PPPOE interface on the mentioned VLAN6.
Connection is created but after 0.2 seconds drops. Then the connection is established again and so on.
Once the connection is established i see the various IP adresses, but only for a short time.
It looks like the link is dropped from the OPENWRT side rather than the provider side, as for some reason OPENWRT thinks that the link is disconnected?

Any suggestions?

Here is the system log:
Fri Jul 29 09:58:19 2022 daemon.notice netifd: Network device 'pppoe-WAN' link is up
Fri Jul 29 09:58:19 2022 daemon.notice netifd: Network alias 'pppoe-WAN' link is up
Fri Jul 29 09:58:19 2022 daemon.notice netifd: Interface 'WAN' is now up
Fri Jul 29 09:58:19 2022 daemon.notice netifd: Interface 'WAN_6' is enabled
Fri Jul 29 09:58:19 2022 daemon.notice netifd: Interface 'WAN_6' has link connectivity
Fri Jul 29 09:58:19 2022 daemon.notice netifd: Interface 'WAN_6' is setting up now
Fri Jul 29 09:58:26 2022 daemon.info pppd[11372]: *No response to 5 echo-requests
Fri Jul 29 09:58:26 2022 daemon.notice pppd[11372]: Serial link appears to be disconnected.
Fri Jul 29 09:58:26 2022 daemon.info pppd[11372]: Connect time 0.2 minutes.

Actually it is after 0.2 minutes

Lcp treshold must be set on other value than 0. Preferably 10..