ANR8336I Verifying label of 3590 volume AD0441 in drive E5632 (/dev/rmt0).
ANR8355E I/O error reading label for volume AD0441 in drive E5632 (/dev/rmt0).
ANR8468I 3590 volume AD0441 dismounted from drive E5632 (/dev/rmt0)
in library CCSO3494.
...

I am running AIX 4.3.3 and TSM 3.7.3 (.8)
3590 E1A (2x) drives
Atape 5.3.9
atldd 4.1.5

Nothing appears in the errpt for the drives after the error.

troubling strangness...

I know you are up-to-snuff on Atape, but anyway it looks related:
from the 3.7.3.8 readme
====================================================================

Customers using 3570 and 3590 drives need to upgrade to at least
Atape 5.3.2.0 level because of changes in the Atape device driver and TSM
to support the IBM Linear Tape Open devices.  With the Atape upgrade, both
the device driver and TSM are synchronized again.

Without the upgrade, existing 3570 and 3590 customers will encounter
harmless but annoying I/O errors during the dismount processing.
The I/O error will be as follows:
ANR8311E An I/O error occurred while accessing drive <drive_name> for
GETLOGSENSE operation, errno = 22.

This error message does not cause the operation to fail.  However, it does
indicate that TSM is not able to obtain diagnostic information from the
3570 and 3590 drives that TSM uses to determine the health of the drive
and the media.
--
Richard
Richard