ipv6 udp query gets no answer

On a server, when I send an udp query via ipv6, it gets no answer.
I tried nslookup, dig, nptdate. If I use ipv4 or tcp over ipv6, response is immediate.
If my server is querying himself, It works aven in udp+ipv6.

ipv4 OK :

@client:~# dig @aaa.bbb.ccc.235 google.com
...
google.com. 300 IN A 172.217.19.14

@client:~# dig @aaa.bbb.ccc.235 google.com AAAA
...
google.com. 300 IN AAAA 2a00:1450:400a:807::200e

ipv6 not good:

@client:~# dig @AAAA:BBBB::235 google.com
; <<>> DiG 9.10.3-P4-Ubuntu <<>> @AAAA:BBBB::235 google.com
; (1 server found)
;; global options: +cmd
;; connection timed out; no servers could be reached

But with tcp:

@client:~# dig @AAAA:BBBB::235 +tcp google.com
; <<>> DiG 9.10.3-P4-Ubuntu <<>> @AAAA:BBBB::235 +tcp google.com
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 21951
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 4, ADDITIONAL: 5

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
;; QUESTION SECTION:
;google.com. IN A

;; ANSWER SECTION:
google.com. 300 IN A 172.217.19.14

The same with ntp:

@client:~# ntpdate aaa.bbb.ccc.188
24 May 12:56:09 ntpdate[26846]: adjust time server aaa.bbb.ccc.188 offset 0.083226 sec

@client:~# ntpdate AAAA:BBBB::188
24 May 12:56:38 ntpdate[27174]: no server suitable for synchronization found