Hal, has this topic been discussed yet?:

One issue people have is the “suddenness” that Kylo switches sides. Granted, we know he’s always been torn between both sides of the conflict, but I do understand that feeling of the reversal of him “going all in.” I think part of that stems with the “Skype” convo when she is in the Star Destroyer. His motivation was for her to turn to the dark side and whatnot. However, since he is wearing the helmet it allows for easier wiggle room to change some aspects of the conversation.

He’s been obsessed with her and wants Rey on his side. In Last Jedi, he wanted her to join him … Forget about everything and everyone, Jedi, Resistance, etc. etc. So what if the dialogue changes to remove the “join the dark side” to just “Join me.” This adjusts his motivation in that scene to focus on the two of them, and not what side to be on. That way, when he later turns, it helps it feel a little more “natural” since it’s not about being in the light or the dark, but now HIM joining with Rey.