Loop on OS6360

[Harry17]

Hello,
I have installed some OS6350 switches in my company and now I have upgraded to OS6360.
I configured the OS6360 the same way as the OS6350 except for the spanning tree which is in flat mode and I have the following problem:
the switch receives the interconnections from our ISP's routers on ports

1/1/23 for voice on vlan 100 and 1/1/24 for data on vlan 1

vlan 1 members port 1/1/24 untagged
vlan 200 members port 1/1/23 untagged (I put vlan 200 to not create a loop on the switch)
vlan 100 members port 1/1/23 tagged

When I connect the 2 interfaces 1/1/23 and 1/1/24 I have like a loop that is created whereas on the OS6350 I do not have this problem.

Do you have any idea of ​​the problem?

Kind regards

[silvio]

change to perVlan-STP at all switches. This is the same like 1x1 at the older switches.
Disable autofabric (maybe you have to disable mvrp for it).
Check if the issue is still there.
BR Silvio