Ok discussed issue with Jens. Signal was indeed omitted on purpose to make it compatible with more Amiga models. We looked together in design of the Indi ECS v1, and there we found an alternative implementation for border blanking without requiring the sync/blank input of the chip. So I've implemented that method in the v2 firmware now. Let me know if that solves the blanking issues you observed.
wow. I had just finished replying to your last post and here you are with a possible fix for Border Blank! Will test it and report back!