Facing issues with collections on EV server.

Dear's,

We have EV for mailbox archiving and have enabled collections on closed partitions for the ease of backup which is working fine.

I had an old closed partition on which collections were not enabled so recently I enabled the collections and found that collections were working fine on it but from last one week i am observing that daily it is collecting only 72 items with 2 files , I did increased the collection time from 15 minutes to 45 minutes but still its collecting only 72 items with 2 files.

What could be the reason that it shows same no. of items getting everyday ?