nftables mangling without NOTRACK: what can happen?

I'm experimenting with stateless NAT using nftables. On the page about statelessly mangling protocol fields, the author says:

Keep in mind the interactions with conntrack, flows with mangled traffic must be untracked

Out of curiosity, what are some of the bad things that can happen if I fail to do this? I can't seem to find any information on this point.


Solution 1:

Connection tracking starts before the mangle table is processed, so the tracked connection would not match the mangled packets, making it useless at best or blocking connectivity at worst.