Sometimes this happens. I do see it on the website, which means there's a chance it will fix itself within a day when the cache expires.

My other advice is often to resave it as a different format. .png and .jpg should both work, but if you're having trouble try making sure it's a .png

ok, yep that works too.

My avatar is through gravatar. We don't really recommend using it these days, but it still works totally fine.