it's a bug.

But the situation causing it can be avoided by using tcp instead of unix for upstream:

config/puma.rb

bind "unix://#{shared_dir}/sockets/puma.sock"

has to be

bind "tcp://0.0.0.0:9292"

nginx/conf/nginx.conf

upstream app {
    server unix:///var/www/reclue/shared/sockets/puma.sock fail_timeout=0;
}

has to be

upstream app {
    server 0.0.0.0:9292;
}

all problems of instability, like they are described in several discussions, disappear. In addition this proves that importmaps is not making anything better. So avoid making things more complicated and simply import js-files directly.