Chain is too long only if it droops or rubs on the underside of the rear derailleur cage when in the small-small combination.So my bike has Ultegra SL and I recently replaced the rings, chain and cassette (12-27). I just replaced all the cables which made no difference with the issue. In the big ring it shifts perfect but not in the small ring. I can adjust the cable and fix it but then the shifting suffers in the big ring. What is going on here? I suspect the rear derailleur may be suspect. Chain line looks good. Chain length might be a tad long but only by a link if that.
First guess would be a derailleur hanger that is not perfectly aligned.