Brocade ICX 7450-48F with a 1G connection to a Cisco device is flapping

[stephen_konig]

Good morning,

The facts:

I have a Brocade ICX 7450-48F switch that is being used as my Distribution Switch for my small network. It has a single 1G connection to a Cisco 3560 via single mode fiber. 

The ICX is configured with 
Port-name
Dual-mode X

The Cisco device is configured with
trunk encapsulation dot1q
switchport trunk native vlan (X to match the ICX)
switchport trunk allowed vlan 1 - X
switchport mode trunk
switchport nonegotiate
mls and qos configurations 

The Issue: The ICX connection to the Cisco device is flapping, meaning I am losing connection to the downstream Cisco device. A Show Log reveals that interface e 1/1/3 is receiving STP State messages for each of my configured VLANS, meaning that each VLAN in the log is cycling through its Listen Learn Forward State 

for example : 

VLAN X Port 1/1/3 STP State -> Listening (MakeFwding)
VLAN X Port 1/1/3 STP State -> Learning (FwDlyExpiry)
VLAN X Port 1/1/3 STP State -> Forwarding (FwDlyExpiry)

I don't understand why STP/BPDU is frequently updating itself causing the interface to bounce. Could this be avoided if I add a second 1G trunk between the ICX and Cisco device? We are not seeing any input or output errors on either side of the link so I didn't want to jump to the possibility that the fiber is dirty.