Question regarding keystore - Cert

I have created a keystore (JKS) and added my cert as pkcs12 with alias-name ubooq_key, as described in https://vaemendis.github.io/ubooquity-doc/pages/tutorials/lets-encrypt.html.

I added the keystore via the admin-page > Security.

When i hit save & restart, page reloads and tells me "Not connected to server".

The "normal" ubooquity-page wants to download a file "download", but the page doesnt show up.

So here my questions: Did i miss a relevant thing regarding the startup-options?

I am serving ubooquity via start-script (running inside a freebsd-jail).

My domain is ubooquity.home.lan.

Changes the port? Mine is set to 80 and 81 for /admin.

I tried with renaming the keystore from keystore to keystore.jks and ubooq_key and finally ubooq_key.jks, every time changing the settings too, restarted the ubooquity server and every time the same errors.

keytool -list shows the cert as valid.

I am running ubooquity 3.0.2.

Thanks very much for any help.