Just a thought here. If the bike started it's life as a 7s, and was converted to 8, they may not have changed out the RD. I've tried using a 7s Chorus RD (with unit with the A/B selector) with Ergo - and it works, sort of, and then it feels out of adjustment. So you readjust it. And you can go through this cycle over and over, but it's never quite right. All was well when I installed a "newer" (8-9s) RD. The 7s units just aren't quite right for Ergo. But close enough to trick you.
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