NDMP sorting file history very slow

Hello,

I have a NDMP backup with NetWorker server version 19.2.1.1 of a Unity share that contains about 30 milions of files for 1 TB of total size that requires about 40 hours for full backup sorting file history. Data backup completes in 4-5 hours. Daily incrementals saves 50-100.000 files in one hour and sorting file history requires 6-7 hours.

There's another file system on the same Unity with 8 milions of files (2 TB) that completes full sorting file history in about 2.5 hours nad incremental sorting file history in less than a minute.

I monitored backup server memory occupation that didn't exceed 75%, disk for indexes and tmp area has 100 GB free. Any idea?