Switching

Pair of EX4650s in virtual chassis, three ports are configured in link aggregation and connected to ISP layer 2 point to point links. Other side is an Alcatel-Lucent OS6900-X48C6. Config excerpt:

interfaces {
     xe-0/0/8 {
        ether-options {
            802.3ad ae2;
        }
    }
    xe-1/0/8 {
        ether-options {
            802.3ad ae2;
        }
    }
    xe-1/0/9 {
        ether-options {
            802.3ad ae2;
        }
    }
    ae2 {
        mtu 9216;
        aggregated-ether-options {
            lacp {
                active;
            }
        }
        unit 0 {
            family ethernet-switching {
                interface-mode trunk;
                vlan {
                    members [ 10 20 30 ];
                }
            }
        }
    }

Prior to upgrade (running 21.4R3-S3.4) it was working fine. After upgrading to the current recommended version (23.4R2-S5.8), the ae2 interface is down (other AEs are working, only this one is affected). The members are up, and I can see the other side's LLDP info on them, but they are not joining the aggregate. As a temporary workaround, I have removed one of them from the aggregate and configured it as a standalone VLAN trunk (on both sides), and traffic is flowing, so the link itself is fine. What steps can be taken to troubleshoot this?