DEC 2750 no traffic for 4-5 minutes after adding VLAN to lagg LACP interface

[Monviech]

Hello,

Setup
I have a DEC2750. The two 10GBit interfaces ax0 and ax1 are connected to a Microtik CRS236-24S+2Q+ with Router OS.

The modules used are Flexoptics SFP+-DAC-Cable 1,5 meter programmed for AXC761 on the DEC2750 side, and programmed for S+DA0001 on the Microtik side.

Problem:
When adding a new VLAN to the lagg interface, both bonded interfaces of the lacp go down for 3 seconds, and then up for 3 seconds. (Can be seen in the logs of the DEC2750 and Microtik).

Even though the lacp and both interfaces are up, the DEC2750 needs around 4 to 5 minutes, until it starts to respond to pings again. During that time there's no layer 3 traffic working.

Trying to replicate the problem with a VM:
I have created a VM in VMware with an opnsense business edition, making the exact same configuration as the hardware firewall. The VM has the same 2x 10Gbit links (Intel X722 for 10GbE SFP+) connected to the same Microtik switch, with the pcie network interfaces passed through directly to the VM. When adding a VLAN in the VM, it works perfectly. There is just a 3 second interruption.

I'm not sure if the DEC2750 Hardware is working the way it should with the LACP protocol. Does anybody else have this problem or a hint for me how to solve this issue?

Thank you very much.