Paul Randal explains a bug in versions of SQL Server 2012 and 2014:
There hasn’t been a case of it failing to reserve enough space until SQL Server 2012, when a bug was introduced. That bug was discovered by someone I was working with in 2015 (which shows just how rare the circumstances are), and at the time it was thought that the bug was confined to the log of tempdb filling up, rollback failing, and the server shutting down.
However, just last week I was contacted by someone running SQL Server 2012 SP3 who’d seen similar symptoms but for a user database this time, and the user database went into recovery.
Read on for details and make sure those SQL Servers are patched.