Prefix "2620:0:X:10::X/128" seen in the database but no in the routing table 

show ospf3 database intra-area-prefix advertising-router 10.255.243.2 detailOSPF3 database, Area 0.0.1.127
 Type       ID               Adv Rtr           Seq         Age  Cksum  Len
IntraArPfx  0.0.0.1          10.255.243.2   0x80009bc9   164  0x266d  52
  Ref-lsa-type Router, Ref-lsa-id 0.0.0.0, Ref-router-id 10.255.243.2
  Prefix-count 1
  Prefix 2620:0:X:10::X/128
    Prefix-options 0x2, Metric 0

show route 2620:0:X:10::X/128
inet6.0: 129 destinations, 129 routes (129 active, 0 holddown, 0 hidden)
Limit/Threshold: 20480/20480 destinations
+ = Active Route, - = Last Active, * = Both

::/0               *[OSPF3/150] 1w0d 01:07:08, metric 0, tag 0
                    >  to fe80::X:X:X:X via ae0.0

Check the "show ospf neighbor" output
LabRouter> show ospf3 neighbor 
ID        Interface       State   Pri  Dead
10.255.243.1  ge-0/0/14.0      Full    1   34
Neighbor-address fe80::X:X:X:5000

10.255.243.2  ge-0/0/26.0      Full    1   38
Neighbor-address fe80::X:X:X:3800         

>> From the output we can see the neighborship to the peer is established via interface ge-0/0/26

Check the "show ospf3 route 10.255.243.2" output 
LabRouter> show ospf3 route 10.255.243.2
Prefix                    Path Route   NH  Metric
                       Type Type    Type
10.255.243.2                Intra Router   IP  55010  
 NH-interface ge-0/0/14.0, NH-addr fe80::X:X:X:5000

>> Looking at the output we can see the "10.255.243.2(lo0 IP of the peer device)" is learned via different interface ge-0/0/14 instead of ge-0/0/26

We shut the interface ge-0/0/14, once we shut the interface we can see the route "10.255.243.2" is learned via correct interface ge-0/0/26 and  the prefix 2620:0:X:10::X/128 installed in the routing table 
 
Shut the interface Ge-0/0/14
LabRouter# set interfaces ge-0/0/14 disable 
LabRouter# commit 
 
Now the route is learned via correct interface ge-0/0/26
LabRouter> show ospf3 route 10.255.243.2 extensive   
Prefix                    Path Route   NH  Metric
                       Type Type    Type
10.255.243.2                Intra Router   IP  60000  
NH-interface ge-0/0/26.0, NH-addr fe80::X:X:X:3800
Area 0.0.1.127, Origin 10.255.243.2, Optional-capability 0x0

The prefix "2620:0:X:10::X/128" is now seen in the routing table 
LabRouter> show route 2620:0:X:10::X/128         
inet6.0: 128 destinations, 128 routes (128 active, 0 holddown, 0 hidden)
Limit/Threshold: 20480/20480 destinations
+ = Active Route, - = Last Active, * = Both
2620:0:X:10::X/128
          *[OSPF3/10] 00:01:39, metric 60000
          > to fe80::X:X:X:3800 via ge-0/0/26.0

The  peer end (different vendor device) had links configured incorrectly to run ospf which caused the prefix to be learned via different interface resulting in the route not getting installed in the routing table.