The MatchX works up and down, no forwarding in fritzbox router 7490 set.
The DIY RPi with dualchannel forwarder from this source https://github.com/bokse001/dual_chan_pkt_fwd is in the same subnet behind the router and works up but not down. Checking UDP packets on port 1700 of the RPi show rxpk, but not txpk. TTN console also shows no downlink traffic.
To ensure TTN routes downlink via the RPi and not the other gateway i switched it off. There is no other gw in range of node, so i expect TTN to use the RPi for downlink, but no txpk on port 1700 of RPi.