MLPPP has stopped working

For some months now on my work connection I've been happily running two Entanet lines with Tomato/MLPPP and 2 Netgear modems in bridged mode, the connection is set up as PPPoE because this is a requirement to be able to bond the two lines.

One of my lines now no longer authenticates when using PPPoE but PPPoA is perfectly fine, is there a solution to my problem without needing to go down the route of load balancing rather than true bonded lines?

Thanks for any suggestions.