This is expected behaviour.
LACP works on hashing algorithm - basically based on L2 / L3 / L4 information from the packet there is a hash of those and based on this the single session goes to one of the pNICs from LACP channel.
Since you have single storage and single hypervisor (iSCSI target / initiator) the traffic will forms only one session thus the session is balanced only through one pNIC.
LACP doesnt double the total bandwith - one session is always limited by speed of one NIC.
Generally I would recommend iSCSI multipathing rather then LACP (in terms of avaliability and balancing of the traffic) but still you will be limited by the speed of single pNIC
First: Thanks for your answer!
Second: So, based on your response i cannot double the speed of ISCSI traffic even if i have more than one NICs? But in what scenario could be usefull to use LACP?
Thanks in advance