Due to a change in the data format provided by the Osmose API, if you
have Osmose enabled (the default), you will experience a crash when
trying to download an area since yesterday.
While I've built a new version that handles the issue (this is simply a
crash avoidance measure, but doesn't address the issue of unexpected
format changes in general, which naturally shouldn't happen), this will
take a while to be available.
The simple workaround for now, and if you are stuck on an old version of
the app, is to disable Osmose downloads. In older versions this can be
found in the "Advanced Preferences" in current versions in the layer
configuration in the layer dialog.