In Safari on my iPad (iOS 10.3.1) I started seeing the grey boxes instead of emoticons in many threads on TMC, starting sometime within the past week.
Then I found this thread... lots of grey boxes. I compared to Safari on my Mac (OS 10.11.6) and to Safari on my iPhone (also iOS 10.3.1) but the emoticons display correctly on both of those . So for some reason only a problem on the iPad. AFAIK there's been no update to Safari on either platform in the timeframe these grey boxes started showing up
I do have a blocker in Safari on both iPhone and iPad (same on both, have been running for many months no trouble, and no recent changes to config). So today on my iPad as a test I did a "reload without content blockers" on this page, and when the page refreshed the emoticons reappeared in place of the grey boxes. After that I reloaded some other threads where I'd seen the grey boxes with blocker back on and emoticons remain correctly displayed now on iPad/Safari. Not sure if just a coincidence and something else happened to change on the site today...