Problem with stack between X250 - X440

[Leonardo_Falcon]

Hello people,
I have two switches in stack.
The switches are X250e-24t and X440-48p.
The version is 15.3.2.11.
This stack has two ports in trunk configured in sharing to the switch core.
The spanning tree is not configured in this network.
One week ago I had a problem because there were a l2 loop.
I think it was a stack problem, causing the misconfiguration of the two ports in sharing and lease two trunk actived.
What do you think?
Are there problems if I do a stack with two platform different?
If I upgrade the version, Can I resolve this problem?
Thank you.

[Karthik_Mohando]

Leonardo, If upgrade is an easy option then i would suggest an upgrade to recommended version of EXOS. Being said this, multiple factors can bring dual master in a stack and if the last one happened due to a code issue then upgrade might fix but not 100% since X250e is the older version of hardware the recommendation is EXOS 15.3.5.2-patch1-10. Here is a link for reference http://www.extremenetworks.com/extreme-hardwaresoftware-compatibility-recommendation-matrices/software-release-recommendations/ If the same issue happens after upgrade then i would suggest to open up a GTAC case to analyze this further.