multicast DNS not propagated

I'm having an issue where mDNS packets are not propagated in my network.
When connecting directly to the access point where the mDNS device is connected to,
it's visible using avahi-browse --all --ignore-local.
But when connecting to the M5 Deco modules, only mDNS devices connected to those are
visible on the network.
Somehow the packets are not propagated between the M5 Decos and our other (TP-link) accesspoint.

model: M5(3.0)
firmware: 1.7.3 Build 20230906 Rel. 59213
- no firmware upgrades available

when opening advanced -> system -> system parameters
- operation failed
- only WAN Unicast is shown with a grayed out 'Enable WAN Unicast'

M5 Deco system is setup in 'Access Point' mode.

Network:
- WAN -> routerA -> M5 Deco -> laptop
                -> accesspointA -> mDNS device

I want to see the mDNS traffic from the laptop, so routerA should forward them from mDNS device -> accesspointA -> routerA -> M5 Dec
o -> laptop.

routerA has wireless disabled
accesspointA has wireless enabled
routerA IP address: 192.168.1.254
M5 Deco IP addresses (DHCP):  
- 192.168.1.68
- 192.168.1.70
- 192.168.1.71
accesspointA IP address: 192.168.1.2

routerA is doing DHCP and is a Nokia-branded device: manufacturer: ALCL, productclass: XS-2426G-B

When connecting to the M5 Deco network, multicast traffic _inside_ that network is available.
Multicast traffic from accesspointA (same subnet) is not available.
When switching from the Decos to accesspointA, multicast traffic from devices connected there is available.

Somehow traffic doesn't seem to be propagated between Deco M5 and accesspointA.
In routerA there don't seem to be much settings available regarding multicast traffic.

Other related topics that I read without resolving this:

about m5 deco:

- deco m5 mdns support: https://community.tp-link.com/en/home/forum/topic/178642
- M5 & TimeMachine: https://community.tp-link.com/en/home/forum/topic/166454
- M5: Should I enable IGMP?: https://community.tp-link.com/en/home/forum/topic/268164
 - Note: Our M5 doesn't show this option
- Problems enabling IGMP snooping on TP-Link deco M5: https://community.tp-link.com/en/home/forum/topic/606116

about other deco products:

- Elgato Key Lights intermittent visibility and controllability when Deco mesh is in Router mode: https://community.tp-link.com/en/h
ome/forum/topic/245872
- Deco X60 mDNS support: https://community.tp-link.com/en/home/forum/topic/236100
- e4 mDNS flood: https://community.tp-link.com/en/home/forum/topic/202160
- Multicast communication is not working: https://community.tp-link.com/en/home/forum/topic/617346

I feel I might be overlooking something here, but I cannot figure out what I'm missing.
They seem to propagate the packets received on them fine,
but somehow they don't propagate any packets coming from the other access point.


related to: multicast, mdns, bonjour, avahi, igmp