Check out the “Let it Snow” Xmas 2020 Group youtube project!”
I was having a similar issue with my A string. The intonation didn't seem right and I couldn't slur notes cleanly on it (it was buzzing). My problem ended up being rosin buildup on the string, as soon as I gave the strings a good cleaning it was back to normal. The other strings had a little rosin buildup too, but only the A was effected. Now I wipe them down every day.