Opentran is database-specific, run it in the database that has the growing log. If your log reuse wait is active transaction, then you have an open transaction.
The number of sessions per login is pretty irrelevant, it's not who's using the system you're interested in, it's who has an open transaction they have not committed. Check DBCC OpenTran, find the spid that it returns, check that spid in sys.dm_exec_sessions and sys.dm_exec_connections to identify who is running it and from where, then decide whether you can get the person to commit the tran (if it's ad-hoc queries) or roll it back after checking what it's doing.
Once you've identified which session has the open transaction, you need to figure out why there is an active transaction every day. Is someone running this manually? Is there a bug in the app? You're going to need to do some investigations.
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