Problem with Buster network

["Roland F.Teichert" <rfteichert@gmail.com>]

Hi all,

I'm using since more then 10 years Debian-Edu in a school. So I will
say thanks to the team for this great work.

But since buster I have a serious problem.

All workstations loose after half an hour their IP address. (it is not
the killer-script)
The syslog tells me:
LehrerPC avahi-daemon[460] :withdrawing address record 10.0.0.2. on eth0
LehrerPC avahi-daemon[460]: Leaving mDNS multicastgroup on interface
eth0.IPv4with address 10.0.0.2

ip addr  shows, there is no IP.
 This happens at all workstation (not the workstation on tjener).
The only solution is a new boot - for another half an hour.

ThinClients are working without any problems.

Does anybody has an idea or a solution?

Greatings,
Roland