After upgrading to 21.02 from 19.07 I have noticed that the WAN speed went from ~900mbps to ~750mbps. I have downgraded and done some benchmarks to confirm that this is indeed the case, here are the results: (note that I was testing it behind another router so the speedtest results have L2NAT, though the outer router's performance doesn't seem to be the bottleneck here. iperf3 only goes through AC58U's NAT). The normal LAN speed is ~940mbps.
speedtest: 838 down 842 up
speedtest: 818 down 828 up
speedtest: 516 down 594 up (something wrong? 25% sirq cpu usage)
speedtest: 760 down 782 up
Was something changed in 21.02 that could've caused this? The latest snapshots also have similar performance to 21.02.