Did you try changing your global miner type from ethminer to claymore and configuring it for the claymore build?  I never tried this on my setup because i had already switched to Simpleminer.net. 
It was just an afterthought when i was looking into what could possibly be different between the two setups (both are Linux based) because i could literally put either usb stick in (Ethos programmed or simple miner programmed) but the Ethos one would not work.

Also - same as you, prior to me looking at adding the 5 more cards - i'd noticed that ethos was crashing more.  Was blaming it on other stuff but maybe that was the issue overall.  I've been up for a little over 24hrs since i switched over and will post how long it goes without having a stability issue or crash.

Cheers.

I tried the switching from Auto to Gen 1 and Gen 2 and still wasn't able to go past the 8th card without a large amount of system instability.  I ended up putting simplemining on a thumb drive and setting it up that way and it worked without issue (was also able to get me hashing up from 27 Mhash/GPU to 29.3 Mhash/GPU. 

I had the global miner in ethos set to ethminer and switched to the latest Claymore in simple mining.  I'm wondering if there is a default setting in Ethminer that only allows for 8 GPU's.  Not too sure.  But it's running now and has been stable for the last couple hours.     

Thanks for the suggestions anyways!

I have a 13 slot H110 Pro BTC+ mother board that has been operating fine for the past couple weeks with 8 GPU's installed on it.
I had intended to install 5 more GPU's on the motherboard but when I go from 8 GPU's to 9 and up; the hashing power on the additional card is halved and the system becomes very unstable. In cases where there were multiple cards above 8 installed, ethos would eventually freeze.

Has anyone had this issue in the past or know what my problem could be? The rig runs without issue at 8 cards but becomes completely unstable afterwards.
Let me know if any other info is needed.

My setup is as follows:
13 - MSI Radeaon RX580 Armor 8G OC (Biosed and running around 27 hash)
ASROCK H110 Pro BTC+ (13 PCI Express Slots)
Running Ethos Version 1.2.7 (Mining Ethereum)
3 - Power supply's with AUX paralleling cables, all Thermaltake Toughpower Gold(2 X 1200W and 1 X 850w)
8GB Ram
PCI-E Powered Riser Adapter Card (16x to 1x Powered Riser Adapter Card / MOLEX to SATA Power Cable - GPU Riser Adapter)

The mother board is all being power off the 850W PSU with separate cables being run for the main ATXPWR1, ATX12V1, PCIE_PWR1, PCIE_PWR2 and SATA_POW1.
I have installed plastic isolators between the PCI riser cables to stop from shorting out and i have checked all the PCI slots and they function correctly just not when installing more than 8 GPU's.

Thanks