Recently there were several cases where the Core got stuck on an older version and then current remote versions started to crash immediately. Probably worth going to the web admin interface of the Nucleus in a browser and verify that the RoonServer version is up to date. The correct current versions are:
Application
Version
Roon / RoonServer
2.0 (build 1211) production
Roon ARC
1.0 (build 145) production
Roon Remote (Android / iOS)
2.0 (build 1211) production
If you have a remote that does not crash, you can start the update for the Nucleus from there in Settings > About. If all your remotes crash, go to the web admin page for the Nucleus and you can initiate the update from there, without needing a remote.