Same I also asked support and they unlocked it for me or just gave me a week of diamond membership.
Anyone else having trouble unlocking achievements?
The incredible happenned with my friend. He got the Achievment "Pen Pal" (friends in 10 different countries) e didn't get "Buddy System"
My home page says I have a 50 day streak, but "Fanatic" (log in 30 days in a row) is not unlocked.
There are automatic streak pauses. So it's possible to maintain a streak after missing days
https://support.chess.com/en/articles/9714718-what-are-streaks

Hi everyone,
I’ve noticed that some achievements on my account haven’t unlocked, even though I’ve clearly met the requirements (e.g. 3D Glasses, Hindsight 20/20, Statistician, and several chess variant-related ones like King of the Hill and Australian Chess).
I’ve already contacted support and sent screenshots, but I wanted to ask here:
Has anyone else experienced the same issue with achievements not unlocking properly?
If so, which ones?
Let’s try to gather everything in one place so Chess.com knows this is not just a single case.
Thanks in advance!