Very slow to establish a TCP connection with the router

I am using macOS 11.4 and padavan firmware on the router. It's quite slow (a few to tens of seconds) when I connect to the router's admin page from macOS, and tcpdump showed that a lot of tcp connections are stuck at the first handshake, the router didn't reply with SYN/ACK after macOS sent SYN. There's no such problem when I connect to the router from another device or visit another website from macOS. Are there special options/headers from macOS' tcp package? ``` 00:48:25.374383 IP mbp.lan.59304 > router.lan.http: Flags [S], seq 1796724219, win 65535, options [mss 1460,nop,wscale 6,nop,nop,TS val 1596083099 ecr 0,sackOK,eol], length 0 00:48:25.475394 IP mbp.lan.59304 > router.lan.http: Flags [S], seq 1796724219, win 65535, options [mss 1460,nop,wscale 6,nop,nop,TS val 1596083200 ecr 0,sackOK,eol], length 0 00:48:25.576576 IP mbp.lan.59304 > router.lan.http: Flags [S], seq 1796724219, win 65535, options [mss 1460,nop,wscale 6,nop,nop,TS val 1596083301 ecr 0,sackOK,eol], length 0 00:48:25.677740 IP mbp.lan.59304 > router.lan.http: Flags [S], seq 1796724219, win 65535, options [mss 1460,nop,wscale 6,nop,nop,TS val 1596083402 ecr 0,sackOK,eol], length 0 00:48:25.778906 IP mbp.lan.59304 > router.lan.http: Flags [S], seq 1796724219, win 65535, options [mss 1460,nop,wscale 6,nop,nop,TS val 1596083503 ecr 0,sackOK,eol], length 0 00:48:25.879255 IP mbp.lan.59304 > router.lan.http: Flags [S], seq 1796724219, win 65535, options [mss 1460,nop,wscale 6,nop,nop,TS val 1596083603 ecr 0,sackOK,eol], length 0 00:48:26.080421 IP mbp.lan.59304 > router.lan.http: Flags [S], seq 1796724219, win 65535, options [mss 1460,nop,wscale 6,nop,nop,TS val 1596083804 ecr 0,sackOK,eol], length 0 00:48:26.481605 IP mbp.lan.59304 > router.lan.http: Flags [S], seq 1796724219, win 65535, options [mss 1460,nop,wscale 6,nop,nop,TS val 1596084205 ecr 0,sackOK,eol], length 0 00:48:27.283921 IP mbp.lan.59304 > router.lan.http: Flags [S], seq 1796724219, win 65535, options [mss 1460,nop,wscale 6,nop,nop,TS val 1596085006 ecr 0,sackOK,eol], length 0 00:48:28.885169 IP mbp.lan.59304 > router.lan.http: Flags [S], seq 1796724219, win 65535, options [mss 1460,nop,wscale 6,nop,nop,TS val 1596086607 ecr 0,sackOK,eol], length 0 00:48:32.086355 IP mbp.lan.59304 > router.lan.http: Flags [S], seq 1796724219, win 65535, options [mss 1460,sackOK,eol], length 0 00:48:32.099170 IP router.lan.http > mbp.lan.59304: Flags [S.], seq 4020057176, ack 1796724220, win 14600, options [mss 1460,nop,nop,sackOK], length 0 00:48:32.099295 IP mbp.lan.59304 > router.lan.http: Flags [.], ack 1, win 65535, length 0 00:48:33.432798 IP mbp.lan.59304 > router.lan.http: Flags [P.], seq 1:2, ack 1, win 65535, length 1: HTTP 00:48:33.466137 IP router.lan.http > mbp.lan.59304: Flags [.], ack 2, win 14600, length 0