dhcpv6 client freeze after Advertise packet

Im trying to get ipv6 address by using dhclient with -6 flag to interface that has connection to dhcpv6 server. When using tcpdump on that interface I can see that the process always freeze after the client gets the advertise packet:

server side:

2018-02-28T19:16:23.886443+00:00 ddd-rrr dhcpd: Solicit message from fe80::ee0d:9aff:fe60:3901 port 546, transaction ID 0x75FBBE00 2018-02- 

28T19:16:23.886908+00:00 ddd-rrr dhcpd: Advertise NA: address 2002:db8:0:1::254 to client with duid 00:01:00:01:02:10:d9:64:ec:0d:9a:60:39:01 iaid = -1704969983 valid for 43200 seconds
2018-02-28T19:16:23.887095+00:00 ddd-rrr dhcpd: Sending Advertise to fe80::ee0d:9aff:fe60:3901 port 546

client side:

03:48:58.916192 IP6 fe80::ee0d:9aff:fe60:3901.dhcpv6-client > 
ff02::1:2.dhcpv6-server: dhcp6 solicit

03:48:58.918246 IP6 fe80::268a:7ff:feb1:b9b0.dhcpv6-server > 
fe80::ee0d:9aff:fe60:3901.dhcpv6-client: dhcp6 advertise

this 2 packets are shown on tcpdump in a loop. can someone explain the behaviour? thanks