Same problem here. But the solution above doesn't work for me. (No lagg in config.xml, adapting vtnet0 accordingly, leads to unassigned interfaces on reboot, when replacing all occurencies accordingly. Manually chaniging only the vlan und pppoe sections does not help either - interfaces assignment works again, but pppoe still does not.)
The PPPoE Client ceased working right after upgrading from 2.4.0 to 2.4.1.
Furthermore - with a backup default gateway, manually configured - package updates fail. e.g. a shell dependency of freeradius3:
https://pkg.pfsense.org/pfSense_v2_4_1_amd64-pfSense_v2_4_1/All/bash-4.4.12_2.txz
Despite name resolution is working here I see a „host not found“ message. I also tried to manually download that from a different client (with wget) and through an LTE connection. All the same pkg.pfsense.org does not exist.
For the PPPoE problem - reinstalled 2.4.1 from it's clean CE iso, restored the config - same error. I reconfigured the pppoe connections from the scratch - same error behaviour.
BTW, there is even more: MTU settings are missing on the "Advanced and MLPPP" tab. I used to have baby jumbo frames configured there.
For the logs: System logs/PPP show setting the MTU, a try to connect and no data. Just as when using the wrong vlan.
I reverted to a virtual disk of 2.3.x - worked all well. I guess 2.4.1 didn't receive sufficient testing. Blame on me.