I've upgraded valet on my macbook (running catalina) and followed the laravel docs including re-running the valet install command and am seeing unexpected 502 Bad Gateway errors. I was checking the logs and found

[27-Aug-2019 20:39:06] ERROR: Another FPM instance seems to already listen on /Users/myuser/.config/valet/valet.sock
[27-Aug-2019 20:39:06] ERROR: Another FPM instance seems to already listen on /Users/myuser/.config/valet/valet.sock
[27-Aug-2019 20:39:06] ERROR: FPM initialization failed
[27-Aug-2019 20:39:06] ERROR: FPM initialization failed
[27-Aug-2019 20:39:17] ERROR: Another FPM instance seems to already listen on /Users/myuser/.config/valet/valet.sock
[27-Aug-2019 20:39:17] ERROR: Another FPM instance seems to already listen on /Users/myuser/.config/valet/valet.sock
[27-Aug-2019 20:39:17] ERROR: FPM initialization failed
[27-Aug-2019 20:39:17] ERROR: FPM initialization failed

It seems there's 3 php-fpm processes running though they all are the same php version (7.3).

Can anyone offer ideas of how to find where the other php-fpm process is being triggered from, and how to fix this issue?

After days of screwing around I found an answer on serverfault that suggested deleting the listening sock. So I ran rm ~/.config/valet/valet.sock and immediately the tailed php log showed

[08-Sep-2019 16:55:48] NOTICE: fpm is running, pid 10316
[08-Sep-2019 16:55:48] NOTICE: ready to handle connections

So I guess that's all there was to it!