Well...chemistry is certainly subjective, so I don't doubt that you didn't see it. However, many people saw it beginning at the end of season 3, including me. So much so that the question about the characters' relationship potential began popping up during Q&A panels right after that and continued through the relationship becoming canon. Both Andrew and Danai have said multiple times that it was among the top questions anyone would ask them when they saw them out and about. Then when you add in the fact that many of the episodes where people point to seeing an especially strong connection between Rick and Michonne were written by Gimple, a lot of people also thought that Jessie came out of the blue, Jessie's character died in the exact same timeframe and the exact same manner as her comic counterpart, the showrunner and writers start outlining the next season so far in advance (like, around the beginning of the year) that they wouldn't have time to see how people responded to Rick and Jessie before they started outlining and writing season 6 and by the time we saw Rick and Jessie finally kiss in the garage, they'd already completed filming the season and it seems more and more likely that Gimple was just telling the truth when he said that. Now, was it executed well? Also up for debate, but I didn't particularly enjoy the execution of the Jessie piece, and while it was clear to me that some significant time had passed in-universe, though it had only been one episode between Jessie dying and Rick and Michonne, it's understandable that others would think it's jarring. I think pacing is a TWD problem in general, though. The mid-season premiere would have worked much better as the finale and then we could come back to "The Next World" with exactly the same amount of time passing for us as it did for the characters, but that's a discussion for another time.