I don't know why it would crash on an old vault, nothing in the underlying database handling has changed. Unless there was a significant difference between plain text storage and what was in the datab...

Just to be clear, nvALT is also open source, https://github.com/ttscoff/nv. Anyone could have updated it at any point in the last 5 years, but nobody did... but it's alive again now, and SimpleNote is...