ext4 won't mount - fsck required - 2nd fsck in less than a week

Hello,

As the subject says, we have a 15 TB fsck drive that won't mount with
these errors:

Sep 9 20:02:20 narf kernel: EXT4-fs (dm-9): ext4_check_descriptors:
Inode bitmap for group 3200 not in group (block 4161027887)!
Sep 9 20:02:20 narf kernel: EXT4-fs (dm-9): group descriptors corrupted!


We did a proactive fsck on Tuesday of last week because it was
starting to give filesystem errors. It ran through and mounted fine.

The filesystem lives on an equallogic SAN spread across 36 drives.
Could this be something with the physical layer or is it not abnormal
to have to run multiple rounds of fsck to fully fix an issue?

Thanks!