BRMS says available tapes "not available"

BRMS is the curse of my existence.

Every morning as I wake up, my first thought is, "Did the backup complete
last night?"

Saturday night the backup failed on LPAR1:

User BRMSOFR in job 751286/BRMSOFR/BRMSWKY started TCP/IP *VIRTUALIP interfac
Interface 10.202.16.7 is active.
Cartridge EVR481 not available.
Cartridge EVR482 not available.
No media of class ULTRIUM3 is available at location TAPMLB01. (C G)
No media of class ULTRIUM3 is available at location TAPMLB01. (C G)
C
No media of class ULTRIUM3 is available at location TAPMLB01. (C G)
Operation ended by media management. Reason code 0003.


Etc. Both tapes mentioned in the job log are indeed present in the tape
library.

The device is varied on. The tape lib is alive and responding to IBM i
commands and to the web interface.

Before the backup on LPAR1, tapes EVR481 and EVR482 showed *EXP and were in
slots in the magazine.

After the failed backup on LPAR1, tapes EVR481 and EVR482 showed in Work
with Media as EJECT. One was in the I/O station; the other was back in its
slot.

Then the backup job ran normally on LPAR2 (a job which starts after the
LPAR1 job starts but would normally run concurrently once started because
the LPAR1 backup is long, 3 tapes). After that, EVR481 and EVR482 in LPR1's
Work with Media view show as *EXP again and neither is any longer in the
I/O station.
Now what?!