@theropologist I see it periodically. I’m primarily using Ivory on a relatively new iPad with lots of memory.

I see it on TL thumbnails as well as the zoom. Oddly, I click on the thumbnail and, just before it drills into the toot, the thumbnail flashes in. Same going back, if the zoom hasn’t loaded.

One more anecdote. A few times I’ve seen it, the source was a Pixelfed account. May be coincidence but I saw it enough that it’s worth considering.