Hardware Compression gets disabled

I have PowerVault Storage 100T DAT72 with Symantec Backup Exec 8.6. My backup job is around 40GB but it was asking for a tape after 36 GB. I downloaded the Tape utility from support and checked for hardware compression status. It said it was disabled. I enabled it and ran the job again. Everything went ok. The next day the job ran automatically and stopped at 36 GB. I checked hardware compression status again, it said disabled. I am using veritas drivers, hardware compression is enabled on backup exec and on backup job. How could I find out why it gets disabled and fix the problem so all the information is compressed and backed up.

thanks for any advice.