Connectivity via OPTO2 cable on RPI4 Lost in troubleshooting

[mol7os]

It worked somehow in the past, but currently I stuck in finding my issue (hopefully someone could help)

Raspberry Pi 4 with original Cable Opto-Link 2 (/dev/ttyUSB0)
Vitoconnect 300 (tried with 300er XML and KW XML files)
Device should be: Vitodens300 with HC1 -> Protocol P300 and KW2

Currently I do not get the terminal connection as I remember from the past:

As Example:
vclient -h 127.0.0.1:3002 -c "debug on",getTempA
debug on:

getTempA:
DEBUG:Thu Sep 12 14:10:15 2024 : Command: getTempA
DEBUG:Thu Sep 12 14:10:15 2024 : Process 3830 tries to aquire lock
DEBUG:Thu Sep 12 14:10:15 2024 : Process 3830 got lock
DEBUG:Thu Sep 12 14:10:15 2024 : >FRAMER: open device /dev/ttyUSB0 ProtocolID 00
DEBUG:Thu Sep 12 14:10:15 2024 : Configuring serial interface /dev/ttyUSB0
DEBUG:Thu Sep 12 14:10:15 2024 : >SENT: 04
DEBUG:Thu Sep 12 14:10:15 2024 : >FRAMER: no preset result
DEBUG:Thu Sep 12 14:10:15 2024 : Waiting for 05
DEBUG:Thu Sep 12 14:10:20 2024 : read timeout
DEBUG:Thu Sep 12 14:10:20 2024 : Error in wait, terminating
DEBUG:Thu Sep 12 14:10:20 2024 : Error executing getTempA
ERR: read timeout
Error in wait, terminating
Error executing getTempA

Example B (telnet)
sudo telnet 127.0.0.1 3002
Trying 127.0.0.1...
Connected to 127.0.0.1.
Escape character is '^]'.
vctrld>debug on
vctrld>getDevType
DEBUG:Thu Sep 12 16:19:40 2024 : Command: getDevType
DEBUG:Thu Sep 12 16:19:40 2024 : Process 2069 tries to aquire lock
DEBUG:Thu Sep 12 16:19:40 2024 : Process 2069 got lock
DEBUG:Thu Sep 12 16:19:40 2024 : >FRAMER: open device /dev/ttyUSB0 ProtocolID 41
DEBUG:Thu Sep 12 16:19:40 2024 : Configuring serial interface /dev/ttyUSB0
DEBUG:Thu Sep 12 16:19:40 2024 : >SENT: 04
DEBUG:Thu Sep 12 16:19:45 2024 : <RECV: read timeout
DEBUG:Thu Sep 12 16:19:45 2024 : <RECV: received
DEBUG:Thu Sep 12 16:19:45 2024 : >FRAMER: framer_reset_actaddr framer_current_addr = FRAMER_LINK_STATUS(15) (was FFFF)
DEBUG:Thu Sep 12 16:19:45 2024 : >FRAMER: close read failure for ack
DEBUG:Thu Sep 12 16:19:45 2024 : >FRAMER: could not set start condition
DEBUG:Thu Sep 12 16:19:45 2024 : Error opening /dev/ttyUSB0
ERR: <RECV: read timeout

FRAMER: close read failure for ack
FRAMER: could not set start condition
Error opening /dev/ttyUSB0
DEBUG:Thu Sep 12 16:19:45 2024 : Process 2069 released lock

sudo /etc/init.d/vcontrol status
● vcontrol.service - LSB: Initscript to start vcontrold deamon
Loaded: loaded (/etc/init.d/vcontrol; generated)
Active: active (running) since Thu 2024-09-12 14:08:31 CEST; 3s ago
Docs: man:systemd-sysv-generator(8)
Process: 3531 ExecStart=/etc/init.d/vcontrol start (code=exited, status=0/SUCCESS)
Tasks: 1 (limit: 3952)
CPU: 182ms
CGroup: /system.slice/vcontrol.service
└─3537 /usr/sbin/vcontrold

Sep 12 14:08:30 pi-home systemd[1]: Starting LSB: Initscript to start vcontrold deamon...
Sep 12 14:08:31 pi-home systemd[1]: Started LSB: Initscript to start vcontrold deamon.

lsusb
Bus 001 Device 003: ID 1a86:7523 QinHeng Electronics CH340 serial converter

USB Settings
sudo stty -F /dev/ttyUSB0 cs8 -parodd cstopb 4800 -ixoff -ixon

I have no idea where to look at, it feels like that my terminal connection via OPTO2 isn´t really working, but how to validate?