I found this happening more often with northbound MBTA services but sometimes a red signal will appear out of nowhere, typically around Route 128, and then cause a traffic jam. I think the patch notes said the glitch was fixed but it seems no
Is this what you were referring to? https://forums.dovetailgames.com/threads/nec-bp-signal-failure.48086/ In any case, in another recent thread about the signalling on NEC-BP, DTG states it is still a work in progress. Hopefully, these are some of the issues that will be addressed