The problem is probably be related to the algorithm you chose for load-sharing.
If you have a server that is accessed from other vlans or the internet, all traffic to/from it will be exchanged between the server mac and the default gateway mac, even though it belongs to multiple sessions and users, and will be sent through one and only one link in the LAG.
If you change it to L3_L4 (enable sharing 9:23 grouping 9:23-24, 9:47-48 algorithm address-based L3_L4 lacp), traffic will be balanced based on the source and destination IP and port and you'll see a better load balancing among the multiple links in the LAG.
Regards, Daniel