Poor Dropbear SSH Implementation?

1.) Ubuntu commandline SSH
2.) Putty (even with Wine on Ubuntu)

1.) However, if I use other clients, like FileZilla with sftp, I get the following error in FileZilla:

Connect with…
fzSftp started, protocol_version=8
open “admin@” 22
Pass: *****
Connected to
Received unexpected end-of-file from SFTP server

2.) Normally I use Ubuntu PAC as a SSH connection manager. This does not work either with the dropbear implementation of ChirpStack OS:
PAC Log:
CONNECTING WITH ‘Gateways - LoRaGateway-01’ (Thu Jul 23 14:00:23 2020) =->
<-= DISCONNECTED (PRESS TO RECONNECT) (Thu Jul 23 14:00:24 2020)

Dropbear log:

Jul 23 12:00:24 raspberrypi4 authpriv.info dropbear[6717]: Child connection from
Jul 23 12:00:24 raspberrypi4 authpriv.info dropbear[6717]: Exit before auth: Exited normally
Jul 23 12:00:26 raspberrypi4 auth.err getty[6736]: tcgetattr: Input/output error^M

I use the latest ChirpStack OS: