Stumped.. AC68U not passing through _some_ clients

[Semantical]

Not really sure how to describe this. I've been away for a couple of weeks, so nothing that I can think could/would have changed and I'm certain it was working.

I have an AC68U as my primary gateway with a LAN IP of 192.168.1.1. DHCP is on, but I have a few statically assigned addresses for various things. ALL wired connections through to the AC68U are made via Devolo powerline adapters (PLA) which work rather well for our house.

Hanging off one PLA is another very basic router (IP 192.168.1.53) setup in bridge mode to go from 192.168.1.0/24 through to 192.168.2.0/24. There are a few boxes on x.x.2.0

From ANY machine connected via WIFi on the AC68U I can ping 1.53 and see the 2.0 subnet.

From two other PLA's I can still see both 1.53 and the 2.0 subnet.

BUT from anything connected to one PLA I can't even ping 1.53 let alone see 2.x. And yet I can see everything else on 192.168.1.0.

There appears to be nothing setup on the bridge to refuse connections from anything. Indeed the IP addresses of devices on the non-working PLA machines are random and span the entire subnet.

I can't see anything on the AC68U which prevents the connection to 1.53 and the routing table looks about right to me

Destination Gateway Genmask Flags Metric Ref Use Type Iface
169.254.0.1 * 255.255.255.255 UH 0 0 0 vlan2
10.0.6.2 * 255.255.255.255 UH 0 0 0 tun21
172.16.12.136 * 255.255.255.255 UH 0 0 0 WAN0 ppp0
10.0.6.0 10.0.6.2 255.255.255.0 UG 0 0 0 tun21
192.168.2.0 192.168.1.53 255.255.255.0 UG 2 0 0 LAN br0
192.168.1.0 * 255.255.255.0 U 0 0 0 LAN br0
169.254.0.0 * 255.255.0.0 U 0 0 0 vlan2
169.254.0.0 * 255.255.0.0 U 0 0 0 MAN0 vlan3880
default 172.16.12.136 0.0.0.0 UG 0 0 0 WAN0 ppp0


Can anyone suggest anything I can look at / try next?