Docker CE cannot load certificate


I am running an instance of seafile on my server. Today the server stopped working and I cannot reach the webinterface.

I do get the following error:
seafile | nginx: [emerg] cannot load certificate “/shared/ssl/mydomain.tld.crt”: PEM_read_bio_X509_AUX() failed (SSL: error:0909006C:PEM routines:get_name:no start line:Expecting: TRUSTED CERTIFICATE)

There seem to be a problem with the SSL cert. I tried the solution given here: Docker CE installation fails to renew certificate already but it does fail.

Does anyone know how to fix this?

Thanks in advance!