RaspberryMatic: HMLANGW mode doesn't work in 3.69.7.20230626

Describe the issue you are experiencing

/bin/hmlangw hangs and endless kernel messages mmd_bidcos: not enough space in buffers appears ~2,5 h after start, no lan gateway functionality at this point.

Describe the behavior you expected

stable lan gateway mode

Steps to reproduce the issue

update from release 3.69.7.20230506 to 3.69.7.20230626 via Web GUI (temporarily rm /usr/local/HMLGW)

What is the version this bug report is based on?

3.69.7.20230626

Which base platform are you running?

Raspberry Pi Zero W Rev. 1.1

Which HomeMatic/homematicIP radio module are you using?

HM-MOD-RPI-PCB

Anything in the logs that might be useful for us?

# netstat -tulpn | grep LISTEN
tcp        0      0 0.0.0.0:22              0.0.0.0:*               LISTEN      1245/sshd [listener
tcp        2      0 0.0.0.0:2000            0.0.0.0:*               LISTEN      1332/hmlangw
tcp        0      0 0.0.0.0:2001            0.0.0.0:*               LISTEN      1332/hmlangw
tcp        0      0 :::22                   :::*                    LISTEN      1245/sshd [listener

# cat /var/log/hmlangw.log 
Client 192.168.178.33 connected to BidCos port!
Client 192.168.178.33 connected to keepalive port!
Keepalive client closed connection.
BidCos client closed connection.

# tail -f /var/log/messages
Jun 28 16:54:10 homematic-raspi-hgw kern.err kernel: [15551.812456] eq3loop: eq3loop_write_master() mmd_bidcos: not enough space in buffers. free space = 15, required space = 18
Jun 28 16:54:10 homematic-raspi-hgw kern.info kernel: [15551.812513] eq3loop: eq3loop_write_master() return error: -14
.
.
. [in endless]

Additional information

Raspberry Pi Zero W is connected by WLAN.

When the issue appears, network between CCU and LAN Gateway still working, but not connected at CCU Web GUI LAN Gateway Configuration page.

On the issued LAN Gateway side the /bin/hmlangw daemon is still running without abnormal CPU load:

# top
.
 1332     1 root     S    20660   4%   1% /bin/hmlangw -n REQ0914234 -s /dev/mmd_bidcos -r -1
.

but I can’t kill 1332 process, means command doesn’t fulfill without any response on CLI.

The Raspberry Pi Zero W doesn’t really hangs, but at issue time its responds very slowly, may be given by the system architecture combined with endless log messages…

To reboot the LAN Gateway solved the issue for next 2,5 hours without any changes on CCU, on release 3.69.7.20230626 too.

Maybe behavior looks like #2340 without any CPU load.

How can I help for further investigations?