Dokku subdomains all point to a single app
This is a domain issue - The wrong value is sent in the 'host' request header.
The lexicographically first site is shown when this is the case. Disable this behaviour so that each site is only shown at the specified domain(s) and nothing is shown at mydomain.net.
To do this, add the following code inside the http section of /etc/nginx/nginx.conf and restart nginx
server { listen 80 default_server; listen [::]:80 default_server; server_name _; return 410; log_not_found off;}Source: http://dokku.viewdocs.io/dokku/configuration/domains/#default-site
Can you copy the output of the following commands?
dokku domains app1dokku domains app2It is possible you added app1.mydomain.net to app2, removed it from app1 or that app1 isn't actually deployed.
Unknown HOST headers are routed to the lexicographically first site in the nginx config stack. Some information about that is available here.
More information about dokku's domain management is available here.