Eureka! It's works.

Put these lines into 

ZXAN(config)#interface gei_0/3/1

ZXAN(config-if)# forward unknown-multicast flood

modify config

config

interface gei_0/1/1

forward unknown-multicast flood

exit

interface gei_0/1/2

forward unknown-multicast flood

exit

I did some test using only c300:

PC ipv6 --- cable --- gbic --- interface gei_1/19/3 --- interface vlan 244 (with ipv6 enable)
From PC ping6 to interface vlan 244 OK!

PC1 ipv6 --- cable --- gbic --- interface gei_1/19/3 --- interface vlan 244 (with ipv6 enable) ---  interface gei_1/19/4 --- gbic --- cable --- PC2 ipv6

ping6 from PC1 to PC2 OK!

So the problem is into F832 ONU.

--------------------------------------------------------------------------------

show running-config
end
configure
 hostname ZTEGB006C2E3_1_6_3_83
 login-security Err-counts 3
 login-security Locking-time 5
 login-security PWdPeriod 0
 login-security PWdRecNum 0
 line auto-pagedown enable
 fan tempContrlFansFlag OFF

 sntp server 192.168.199.250
 time-zone 1
 snmp-server host 192.168.199.250 zte-nms
end
configure vlan database
  vlan 2-4093
end
configure vlan 1
  addport gei_0/1/1-24 untag
  addport gei_0/3/1 tag
end
configure vlan 2
  addport gei_0/3/1 tag
end
configure vlan 3
  addport gei_0/3/1 tag
end
configure vlan 4
  addport gei_0/3/1 tag
end
[..removed for summary..]

configure vlan 32
  addport gei_0/3/2-5 tag
end

[...removed for summary...]

configure interface gei_0/3/2
   qos trust cos
   switchport default vlan 32
end

configure interface gei_0/3/3
   qos trust cos
   switchport default vlan 232
end

[...removed for summary...]

configure
 eth-switch port-protect disable
end
ag
 mod-mgbaseattr mgid 1 protype 3 
 mod-sipuseragent uaid 1 uaip 192.168.1.10 uamask 255.255.255.0 port 5060 proxyindex1 1 
 mod-ntimer parid 292 name NamedTimer292 orginal 292 current 292
 mod-ntimer parid 293 name NamedTimer293 orginal 293 current 293
 mod-ntimer parid 294 used 0 name NamedTimer294 orginal 294 current 294
 mod-mgcattr mgctype 8 maxtransinpkg 3 
 mod-ipstermid tmidfix RTP/000 type 3 digitlen 2 begno 0 mgid 1

Thanks.

C300 version details:

#show version-running
PhyLoc  FileType   VerType    VerTag            BuildTime           VerLength
-------------------------------------------------------------------------------
1/1/6   GTXK       MVR        V2.1.0            2017-07-03 00:28:55 7481408
1/1/6   GTXK       BT         V4.0.14           2017-09-04  0:52:45 524288
1/1/10  SCTMB      MVR        V2.1.0            2018-01-25 15:54:35 35950309
1/1/10  SCTMB      BT         V4.0.11           2016-06-27 15:52:50 333440
1/1/10  SCTMB      FW         V2.1.0            2018-01-25 15:54:51 1906587
1/1/11  SCTMB      MVR        V2.1.0            2018-01-25 15:54:35 35950309
1/1/11  SCTMB      BT         V4.0.11           2016-06-27 15:52:50 333440
1/1/11  SCTMB      FW         V2.1.0            2018-01-25 15:54:51 1906587
1/1/18  CICK       MVR        V2.1.0            2017-01-17 00:36:30 2895056
1/1/18  CICK       BT         V1.0.0P2          2012-07-23 17:22:21 330092
1/1/19  HUTQB      MVR        V2.1.0            2016-12-16 03:17:47 3025408
1/1/19  HUTQB      BT         V4.0.16           2017-12-11  0:47:09 265072
1/1/20  HUTQB      MVR        V2.1.0            2016-12-16 03:17:47 3025408
1/1/20  HUTQB      BT         V4.0.16           2017-12-11  0:47:09 265072

F832 version details:

ZTEGB006C2E3_1_6_3_83>show version
CardType Type VerNo            VerLen   Status BuildTime      State     FileName
--------------------------------------------------------------------------------
Current Running MVER Info:
M24G     MVER V1.1.1           8250747  VALID  20210306015007 running


Saved Versions'  Info on flash:
M24G     MVER V1.1.0P4         9008376  VALID  20170821141149 backup M24G.bak
M24G     MVER V1.1.1           8250747  VALID  20210306015007 active M24G.bin
XGQX     FW   V2.0.0P1         7841648  VALID  20191217152801 active XGQX.bin
BXGQX    FW   V2.0.0P1         528448   VALID  20191217152802 active BXGQX.bin
M24G     SVER V1.1.1           2060708  VALID  20210306015007 active M24G_SV.bin


Current Boot Info:
M24G     BOOT V1.1.1           383208   VALID  20210306014920 active
Current Chip Info: 0X0000000A
--------------------------------------------------------------------------------

If the IPV6 address is configured in the VLAN of the C300 for the ping test, pay attention to the following description.
1. The C300 can transparently transmit IPV6 packets. If the address of IPV6 is enabled on the C300, the software version and main control board model of the C300 should be considered.
2. F832 also supports transparent transmission of IPV6 packets. To enable IPV6 address, the software version needs to be considered. Are PC1 and PC2 connected to the two LAN interfaces of the same F832 equipment? Is the uplink interface of F832 configured with ZXAN(config-if)# forward unknown-multicast flood.

two pc connect onu lan 1 and lan 2,then ping test 

Therefore,
The problem has nothing to do with C300.
Please provide F832 of the following information:

show card

show running-config