@thilobi
Please try and add
exmdb_listen = [::1]:5000 127.0.0.1:5000 to gromox.cfg
consequently removing deprecated exmdb_listen_portand listen_ip
The default for exmdb_listen here is [::1]:5000, which effectively disables connects on the IPV4 interface.
If your localhost resolves to an IPV4 address, connects to localhost:5000 will fail with the default-settings.
Just my 50cts, but I was able to reproduce your issue in a similar manner.