Problem with JACK over network on Win10

[halbius]

Describe the bug

I am running two machines with Win10. Last time I used JACK a few months ago I had both machines connected with JACK via networked, everything worked fine. For setup I followed this guide
But the machines don't connect anymore. Jack seems to start, but on the slave it says "Waiting for Master"

Environment

• JACK Version: JACK 1.9.22
• Operating System: Windows 10 Pro, Audiointerface RME Fireface (Master)
• Installation: binary from the JACK homepage

Steps To Reproduce

On the master I start Jack via qJackCtl.
In the setup in the options tab I use 'jack_load netmanager' in the "Execute script after startup".
It starts and I can connect applications.
On the slave I start jack via qJackCtl, selecting "net" as driver.
I also tried "netone" but it says

netjack-poll not implemented
Waiting aborted
Initing net driver fails

The network itself works fine, I can access both machines via ping and other stuff like file exchange, kvm, etc.
For jackd.exe I added firewall rules allowing all protocols and ports in both directions on both machines.

Then I saw there are some error messages in qJackCtl at startup:

Drivers/internals found in : C:\Program Files\JACK2
jack_get_descriptor : dll jack_inprocess.dll is not a driver
jack_get_descriptor returns null for 'jack_inprocess.dll'
jack_get_descriptor : dll jack_internal_metro.dll is not a driver
jack_get_descriptor returns null for 'jack_internal_metro.dll'
jack_get_descriptor : dll jack_intime.dll is not a driver
jack_get_descriptor returns null for 'jack_intime.dll'
Drivers/internals found in : C:\Program Files\JACK2
JACK server starting in realtime mode with priority 10
self-connect-mode is "Ignore all self connect requests"
Cannot connect to named pipe after wait = \\.\pipe\server_jack_default_0 err = 2
Cannot connect to server request channel
jack server is not running or cannot be started
JackShmReadWritePtr::~JackShmReadWritePtr - Init not done for -1, skipping unlock
JackShmReadWritePtr::~JackShmReadWritePtr - Init not done for -1, skipping unlock
jack_deactivate called with a NULL client
jack_deactivate called with a NULL client
jack_client_close called with a NULL client

It does not seem to have any effect on Jack working, as other apps are recognized by JACK and I can connect them.
I found out that others had the same problem (for example #937).
I tried all the solutions, but nothing helped.
Don't know if this has anything to do with the net problem?

I desperately hope anyone can help me getting this network stuff working again...?

Expected vs. actual behavior

Last time I used this setup everything workes fine, I could connect both machines.
But now for some reason it does not work anymore