Android devices don't get IPv6 default route

Hello,

I’ve noticed a problem since last (or last but one) package update batch, that my Android devices: smartphones and Android TV have stopped receiving IPv6 default route (from router advertisement), but still get IPv6 address (because IPv6 prefix is advertised and IPv6 DNS resolver address (same).

So the end effect is the following resolver list (in that order):
my_ipv6_prefix::1
192.168.2.1 (I changed subnet)

The end result is, all domain resolutions suffer from extremely long latency. I looked into configs and tcpdump, but nothing obvious come to my mind.

If someone knows the answer to how to fix it, I would be very grateful.

This is what Wireshark decodes on the RA packet:

Frame 19670: 230 bytes on wire (1840 bits), 230 bytes captured (1840 bits) on interface 0
Ethernet II, Src: CzNicZSP_00:74:b2 (d8:58:d7:00:74:b2), Dst: IPv6mcast_01 (33:33:00:00:00:01)
Internet Protocol Version 6, Src: fe80::da58:d7ff:fe00:74b2, Dst: ff02::1
Internet Control Message Protocol v6
    Type: Router Advertisement (134)
    Code: 0
    Checksum: 0x2016 [correct]
    [Checksum Status: Good]
    Cur hop limit: 64
    Flags: 0xc0
    Router lifetime (s): 1800
    Reachable time (ms): 0
    Retrans timer (ms): 0
    ICMPv6 Option (Source link-layer address : d8:58:d7:00:74:b2)
        Type: Source link-layer address (1)
        Length: 1 (8 bytes)
        Link-layer address: CzNicZSP_00:74:b2 (d8:58:d7:00:74:b2)
    ICMPv6 Option (MTU : 1280)
        Type: MTU (5)
        Length: 1 (8 bytes)
        Reserved
        MTU: 1280
    ICMPv6 Option (Prefix information : 2001:470:6bc6::/64)
        Type: Prefix information (3)
        Length: 4 (32 bytes)
        Prefix Length: 64
        Flag: 0xc0
        Valid Lifetime: 7200
        Preferred Lifetime: 1800
        Reserved
        Prefix: 2001:470:6bc6::
    ICMPv6 Option (Prefix information : fd80:daaf:bccc::/64)
        Type: Prefix information (3)
        Length: 4 (32 bytes)
        Prefix Length: 64
        Flag: 0xc0
        Valid Lifetime: 7200
        Preferred Lifetime: 1800
        Reserved
        Prefix: fd80:daaf:bccc::
    ICMPv6 Option (Route Information : Medium 2001:470:6bc6::/48)
        Type: Route Information (24)
        Length: 3 (24 bytes)
        Prefix Length: 48
        Flag: 0x00
        Route Lifetime: 7200
        Prefix: 2001:470:6bc6::
    ICMPv6 Option (Route Information : Medium fd80:daaf:bccc::/48)
        Type: Route Information (24)
        Length: 3 (24 bytes)
        Prefix Length: 48
        Flag: 0x00
        Route Lifetime: 7200
        Prefix: fd80:daaf:bccc::
    ICMPv6 Option (Recursive DNS Server 2001:470:6bc6::1)
        Type: Recursive DNS Server (25)
        Length: 3 (24 bytes)
        Reserved
        Lifetime: 1800
        Recursive DNS Servers: 2001:470:6bc6::1
    ICMPv6 Option (Advertisement Interval : 600000)
        Type: Advertisement Interval (7)
        Length: 1 (8 bytes)
        Reserved
        Advertisement Interval: 600000