Update to 2.4.15.
From install-upgrade:
Upgrading from 2.4.14
* We recommend that ALL sites with fulldirhash enabled run
tools/rehash on their mail spools after upgrading from 2.4.14.
There were serious 32 vs 64 bit hashing bugs which were made worse
with 2.4.14. NOTE: the syntax of tools/rehash has changed. Run it
without arguments to see a usage statement.