If statistics are out of date, that does NOT mean that they aren't being used, that typically means that the table they are on is large enough that SQL Server's built in rule about only autoupdating statistics after 20% modifications doesn't kick in frequently enough.  If a table has 10,000,000 rows in it, autoupdate of statistics won't happen until after 2,000,000 rows have been inserted/updated.
https://www.sqlskills.com/blogs/erin/understanding-when-statistics-will-automatically-update/

There were some changes to this behavior introduced in SQL Server 2016:
https://www.brentozar.com/archive/2016/03/changes-to-auto-update-stats-thresholds-in-sql-server-2016/