I won't comment on your config from a general perspective as there may be other things to organize/cleanup but to answer your question directly. The following rules are not specific enough, you are marking all traffic that is coming in from the WAN interface to any destination (which can only be any other network, in your case this is LAN) as download. This may be fine for your situaiton but I would argue you want to add an "out-interface" filter to ensure you are only makring packets that are trully considered downloading. Similarly you are marking all packets that are originating from your LAN network (in-interface = LAN) to any destination as upload. This would be true in the case you never had LAN -> LAN traffic (often called east - west traffic). This is why you are experiencing the issue you are facing, to fix it, simply do the below.
The key changes are adding the out-interface lists and use forward chain since your traffic is not destined for the router.
Code:
/ip firewall mangleadd action=mark-packet chain=forward in-interface-list=WAN out-interface-list=LAN \ new-packet-mark=download passthrough=yesadd action=mark-packet chain=forward in-interface-list=LAN out-interface-list=WAN \ new-packet-mark=upload passthrough=yesStatistics: Posted by blacksnow — Mon Mar 18, 2024 2:50 pm