Some people have a real habit of using the word “but”, however they need to be aware of what the word means to the other party on the receiving end. If someone is trying to explain themselves and you understand or agree to a certain extent, then using the word “but” in your response could be translated as “everything that I said before the word ‘but’ is inconsequential or even untrue- get ready for what I really mean!!”
As a simple example this would sound something like “I appreciate that that's your perspective and I think there's some merit in it, but I think that there's a much better way of looking at this”- as soon as the person hears the word “but” in that sentence, they may interpret it as the short form of “I don't appreciate your perspective and I don't think there's any merit in it”.
Keep an eye on how and when you use the word ‘but’ and consider using it less, or at the very least spending a bit more time on being genuinely positive about the other person’s perspective. Before you move on too quickly to counter their position try asking an open-ended question to further explore and understand their viewpoint - it’s a great segue into you presenting your side of the story.