Both tempdb and database transacton log full

Question

We saw some substantial log growth on both tempdb and one of the user databases. Our database is in Snapshot isolation and we take transaction log backups every 15 minute.

First 'TL log full error 9002' happened at 12.03, 2 minutes after the tl backups were taken. TLs of both the database and the tempdb stated to grow at this point. I think most of the transactions resulted in the error (in between all the scheduled jobs like reindexing and some other jobs that processes data are successfully completed).

Error log entered over 8 million entries of Error 9002 for the next 12 hours till the tl log size reached the max filesize). I go through all the error logs both sql and windows-which doesn't show any information other than the error messages "The transaction log for database 'abcd' is full due to 'ACTIVE_TRANSACTION'.".

I appreciate if someone can guide me in the proper direction to find the culprit.