We've had a few reports over the last few months where Sql Server LocalDB sometimes crashes. It's not a problem with Relatude or caused by Relatude, but when we finally got the error ourselves, we needed to find a solution. The problem is that neither a restart of SQL Server or the machine fixes the problem.
After a while, we found a solution that fixes the problem in all the cases we've had.
The error you often get is "Cannot open database "DATABASE NAME" requested by the login. The login failed. Login failed for user XYZ".
A blog post at Code Project describes the fix: