Found it!
https://git.openwrt.org/?p=openwrt/openwrt.git;a=commit;h=f0cc5f6c0a72b7da9ed5915cf561e2f81d514c68
This commit breaks PPPoE. With the one before it works perfectly.
Sent a mail to @nbd with logs.
MOD: if I revert this single commit, latest snapshot starts to work just fine.