Hi Zsolt,
I don't believe EXOS supports lossless recovery for LACP.
I would recommend you to try some actions (if not yet done) like:
- Change the Linux Ubuntu machines from passive to active mode
- Change the sharing algorithm in EXOS from l2 to l3_l4 (you will need to delete and create the LAG again)
- Change the lacp timeout from long to short
configure sharing lacp timeout short
Note: Since the issue is related when the port goes down/up, LACP timeout might not fix the issue, but I think it's worth a try.