Network connection interrupted for a short time since upgrade to Big Sur

I just made the upgrade to Big Sur 11.0.1 on my late 2015 iMac 27"

All worked fine so far. But since the upgrade I noticed, that my Network connection from the iMac gets disrupted always around noon. My whole network works fine (have my Home Office Laptop active etc.) the iMac shows it is connected to my WLAN but I can't access any webpages anymore.

ifconfig shows en1 up and running but ping fails to my router:

en1: flags=8863<UP,BROADCAST,SMART,RUNNING,SIMPLEX,MULTICAST> mtu 1500

options=400<CHANNEL_IO>

ether 28:f0:76:24:39:32 

inet6 fe80::1051:6ddc:2297:ffb9%en1 prefixlen 64 secured scopeid 0x5 

inet 192.168.1.26 netmask 0xffffff00 broadcast 192.168.1.255

inet6 2001:16b8:22f3:9b00:14d5:b0f2:66a5:d53a prefixlen 64 autoconf secured 

inet6 2001:16b8:22f3:9b00:e5fc:55eb:cbde:c26b prefixlen 64 autoconf temporary 

nd6 options=201<PERFORMNUD,DAD>

media: autoselect

status: active

BIGMEKs-iMac-764:~ Bigmek1$ ping 192.168.1.1

PING 192.168.1.1 (192.168.1.1): 56 data bytes

Request timeout for icmp_seq 0

Request timeout for icmp_seq 1

Request timeout for icmp_seq 2

Request timeout for icmp_seq 3

Request timeout for icmp_seq 4

I can either wait a while or do a ifconfig en1 down / up and it works again.

I have never had this before and other devices (iphone / ipad / Windows PC) show no such problems, so I am really sure, this is related to the Big Sur upgrade somehow.

Anyone else got such issues ?