I have an IBM T420 running Ubuntu 24.04.

The wifi acts weird: Over time it slows to a crawl, but if I
disconnect and reconnect then the speed recovers to the expected
speed.

This is not a fluke: You might expect the wifi or my internet
connection to be overloaded now and then, but this is reproducible.

It sometime recover the speed by itself, but it is reproducible: Any
time it is slow, simply reconnect wifi and the speed recovers.

I did this `timeout 10 tcpdump -ni all` before and after reconnecting
wifi.

Note how the maximal time between packets is huge in the slow
situation (number in ms since last packet):

    $ grep -v lo tcpdump.slow.txt |
        perl -pe 's/://g; s/^(\S+)/($1-$last)*1000/e;$last=$1;s/win.*//' |
	sort -n | head -n -1 | tail
    138.347000000067 wlp3s0 Out IP 192.168.100.133.53472 > 192.168.100.1.53 16660+ [1au] A? www.youtube.com. (44)
    143.536000003223 wlp3s0 In  IP 91.189.91.42.443 > 192.168.100.133.41830 Flags [.], seq 3920040600, ack 1, 
    145.438999999897 wlp3s0 In  IP 172.217.145.198.443 > 192.168.100.133.33518 Flags [.], seq 217117218513, ack 4, 
    161.396000010427 wlp3s0 In  IP 91.189.91.42.443 > 192.168.100.133.41830 Flags [.], seq 1400015400, ack 1, 
    163.872000004631 wlp3s0 In  IP 172.217.145.198.443 > 192.168.100.133.33518 Flags [.], seq 9287394269, ack 4, 
    209.784000006039 wlp3s0 In  IP 172.217.145.198.443 > 192.168.100.133.33518 Flags [P.], seq 4401345409, ack 4, 
    230.691000004299 wlp3s0 In  IP 91.189.91.42.443 > 192.168.100.133.41830 Flags [.], seq 42949602964294961696, ack 1, 
    239.476000002469 wlp3s0 In  IP 172.217.145.198.443 > 192.168.100.133.33518 Flags [.], seq 2028121677, ack 4, 
    244.7780000075 wlp3s0 In  IP 91.189.91.42.443 > 192.168.100.133.41830 Flags [.], seq 1540016800, ack 1, 
    453.129999994417 wlp3s0 In  IP 91.189.91.42.443 > 192.168.100.133.41830 Flags [.], seq 23102893132310290713, ack 3045969685, 

But small in the fast situation:

    $ grep -v lo tcpdump.fast.txt |
        perl -pe 's/://g; s/^(\S+)/($1-$last)*1000/e;$last=$1;s/win.*//' |
	sort -n | head -n -1 | tail
    14.2179999966174 wlp3s0 In  IP 122.2.214.142.443 > 192.168.100.133.48242 Flags [F.], seq 205202, ack 1933, 
    14.4089999957941 wlp3s0 In  IP 91.189.91.42.443 > 192.168.100.133.41830 Flags [.], seq 7000071400, ack 1, 
    15.348000000813 wlp3s0 In  IP 91.189.91.42.443 > 192.168.100.133.41830 Flags [.], seq 922600924000, ack 1, 
    15.8539999974892 wlp3s0 In  IP 122.2.214.142.443 > 192.168.100.133.48218 Flags [.], ack 1931, 
    18.1480000028387 wlp3s0 In  IP 202.138.160.143.443 > 192.168.100.133.58298 Flags [.], seq 131932133332, ack 1936, 
    19.9160000047414 wlp3s0 In  IP 122.2.214.142.443 > 192.168.100.133.48262 Flags [.], seq 3640537805, ack 1932, 
    24.6269999915967 wlp3s0 In  IP 91.189.91.42.443 > 192.168.100.133.41830 Flags [.], seq 1960021000, ack 1, 
    29.4679999933578 wlp3s0 In  IP 202.138.160.143.443 > 192.168.100.133.56522 Flags [F.], seq 5944, ack 1936, 
    33.2009999983711 wlp3s0 In  IP 202.138.160.143.443 > 192.168.100.133.56522 Flags [.], ack 1936, 
    120.297000001301 wlp3s0 In  IP 202.138.160.143.443 > 192.168.100.133.56522 Flags [P.], seq 42014531, ack 518, 

What causes this?

https://git.data.coop/tange/Test/src/branch/main/slow-wifi

dmesg.txt
- dmesg entries when reconnecting wifi

iwconfig.txt
- ifconfig -a

lspci.txt:
- lscpi

lsusb.txt
- lsusb

uname:
- uname -a

tcpdump.slow.txt:
- Download big YouTube videos
- Wait until wifi is slow
- timeout 10 tcpdump -ni all 
- 884 packets

tcpdump.fast.txt:
- Continue downloading big YouTube videos
- Disconnect and reconnect wifi (done immediately after slow)
- timeout 10 tcpdump -ni all 
- 32029 packets