Was this database part of an availability group? There's a thing about lazy recycling of transaction log VLFs that might be what's causing problems / concerns. https://blogs.msdn.microsoft.com/sql_pfe_blog/2013/06/27/lazy-log-truncation-clearing-of-sql-transaction-log-vlf-status-deferred/
Thomas Rushton
blog: https://thelonedba.wordpress.com