SQL Server database in Recovery mode, how to troubleshoot?

I have a SAP instance running with a 'SQL Server' database that just recently got into recovery mode without a clear reason (no backup or restore was executed). We noticed that the storage for logs (max 50gb) was 99% used. After cleaning unused data and turning the db to online, everything was back to normal. But I need to identify the root cause. What can you suggest, please, as a troubleshoot analysis approach? More details: `MSSQL release 12.00.6329.01 DB Client Library msodbcsql13 Database Releases MSSQL 9.00.2047 or higher` It's connected to SAP system via Database Shared Library: `DBSL Version 753.02 DBSL Patch Level 510 SQL Server 2014 120`