ICX Stack LAG Issues

[Dr_Kosmos]

We have an issues with a ICX 7550 Stacks where traffic seems to be discarded.

The stack have a Firewall connected with a LAG with one connection per Stack Unit.We also have a LAG from this stack to another ICX 7550 Stack which acts as dist switches for all the access switches.
Traffic in the primary stack that flows through the LACP port to the secondary unit seems to be discarded and we encounter intermittent traffic flow.
To solve this issue we've been forced to disable the ports on the secondary unit. 

The issue also occurs when the firewall is connected only using one port to the primary unit. And the dist switches are connected to both the primary and secondary units. So when traffic flows through the secondary unit it seems to disappear.

We've setup both the stacks with 2x40Gig DAC- Cables.

Stack config

ver 09.0.10h_cd2T241
!
stack unit 1
unit-name sw01-1
module 1 icx7550-24f-port-management-module
module 2 icx7550-100g-2port-200g-module
priority 255
stack-trunk ethernet 1/2/1 to 1/2/2
stack unit 2
unit-name sw01-2
module 1 icx7550-24f-port-management-module
module 2 icx7550-100g-2port-200g-module
priority 240
stack-trunk ethernet 2/2/1 to 2/2/2
stack enable
stack mac d4bd.4f36.33b0
!
hitless-failover enable
!

Lag Configs

lag FW-LAG1 dynamic id 1
ports ethe 1/1/15 ethe 2/1/15
port-name FW1-X1 ethernet 1/1/15
port-name FW1-X2 ethernet 2/1/15
disable ethe 2/1/15

!
lag EDS dynamic id 4
ports ethe 1/1/23 ethe 2/1/23
port-name LACP_SW ethernet 1/1/23
port-name LACP_SW ethernet 2/1/23
disable ethe 2/1/23
!

All help is appreciated.
We belive that the stack configuration is correct and we suspect that there might be some other, maybe hardware related issues with stack unit number two.

We've tried and replaced the DAC Cables. 
Tried firmware 8.0.95 now runs 9.0.10h