The actual cause of transaction log full under below scenario
First of all do what the message says and run 

SELECT log_reuse_wait_desc FROM sys.databases WHERE name = 'your db name'


I'd also check sys.database_files in your database to confirm the actual settings for the transaction log file.

Once you have the reuse identifier then check it against the values at https://docs.microsoft.com/en-us/sql/relational-databases/system-catalog-views/sys-databases-transact-sql?view=sql-server-2017