I've been having the same issue with posters avatars being missing. At one point about half of them didn't show up and right now it is only a few. I noticed Snoopy's and Skate Talker's avatars have been missing for a couple of days. I run programs every day to clear cookies and temporary files and a defrag program but it doesn't get rid of the problem. I had the same problem back in August and then it just cleared up and now it is back.
I'm running Windows 7 with updated Chrome browser.
It's not the same avatars every time. I can see ones today that I couldn't see yesterday, but different ones are missing.
It just seems to be an issue on my PC. I was on my iPad using Safari earlier and it was fine. I thought it might be a Chrome issue, so I loaded the page in Edge. The front page looks fine there, but as soon as I go into a sub-forum some of the avatars down the side of the thread titles are missing. Avatars are appearing in the thread itself though.