Can't delete measures, but saving/reloading fixes it
No, I can't include a score that behaves this way, because the instant you save it and reload it, it doesn't happen. This has happened occasionally for a long time in MS3 -- just happened again in 3.4 beta. I select measures the usual way, and both ctrl-delete and Tools > Remove Selected Range just don't do it. I have no idea what situation brings it about. This was the simplest possible score, 32 measures of a single vocal line, half of whose measures I didn't need and wanted to delete.