I discovered a bug in Lightroom!
If you apply the spot heal tool to an area in a RAW file (in this case, a Sony ARW one) and convert it to lossy DNG the spot heal will become a pink square. It’s easily fixed by applying the spot heal again but of course this shouldn’t happen.
While on the subject of Lightroom bugs, a long time ago I also noticed that the Transform tool acted differently on the compressed DNG version of a photo compared to the RAW (CR2) version. Hopefully that’s been fixed because that was a couple of years ago and I’m sure someone else has noticed by now ..