I upgraded from 6.6.7 to 6.7 at the same time I made some other changes, and the system would reliably stop responding within 1 to 8 hours. One of the other changes was replacing a failing drive and rebuilding the array, so I eventually backed out every other change but that one. Each time I would bring up the server, it would try and rebuild the replaced drive, but stop responding before it completed. It wasn't crashing, as the lights were still on, but there was no disk activity. I tried to rebuild the drive at least 8 times on 6.7, but it never completed. I finally rolled back to 6.6.7 last night and the rebuild completed and the server is running normally. There were never any errors reported on 6.7 and one of the rebuilds was with all plugins disabled. It passed Memtest multiple times, and the VM and docker apps were not running during the rebuild.
Here's the build details, the hardware isn't especially new:
M/B: ASRock - 970 Extreme4
CPU: AMD FX-8320E
RAM: 16GB DDR3 1600
Case: Norco 4224
Controllers: LSI SAS1068E & SAS2008
Drives: 16 data + dual parity, cache + 2 outside array for docker / vm
Apps: MythTV VM and Plex docker
NICs: onboard Realtek RTL8111E + PCIe BCM5721 (bonded), and PCI Intel PRO/1000 (vm)
I waited before rolling back as I had initially added another SAS1068E that might be bad and accidentally reset the BIOS settings, but the system hangs continued after correcting both of those.