Something has gone very wrong with clustering in most recent release. I haven't got to the bottom of it yet, but even if I drag in a relatively small set of files; say 300 or so, then cluster them all it will frequently stop at various places and fail to cluster a portion of the files in unmatched files.
After it has stopped the first time, if you press cluster again it will start again, but also stopping multiple times. It seems to get worse and worse the more often it stops, actually. It's extremely irritating because if it has stuck halfway through the files for one cluster you end up with 2+ clusters afterwards since clustering doesn't take into account existing clusters when deciding how to cluster a new chunk of unmatched files.
This feels like some kind of threading issue to me.
Although haven't done much background research yet, I'm logging this here in case others are having the same problems.