Configure HA - "hauser" filed to login

Hi there

We're trying to set up a High availability environment (active-passive) using this documentation: https://docs.sophos.com/nsg/sophos-firewall/19.0/Help/en-us/webhelp/onlinehelp/HighAvailablityStartupGuide/HAConfiguration/HAQuickHAConfigureActivePassive/index.html

Both Firewalls are on Firmware SFOS 19.0.1 MR-1-Build365.
Both Firewalls have the same Passphrase for HA.
The HA-Ports are configured as DMZ and they're in the same Subnet (but with different IPs).
The HA-Port is the same on both Firewalls.
After initiating the HA, the primary device always just shows that he's trying to connect to the auxilary device, but nothing more happens (we've waited for at least 10 minutes).

On the auxilary device in the admin log, we can see the message:
User 'hauser' failed to login from 'IP of the primary device' using ssh because of wrong credentials

So we changed the Passphrase, but that didn't change anything.
The admin log still shows the failed log in from hauser.

What else can we check to be sure that hauser have the correct credentials?

Greetings
Rexer