Hi,
after updating to Nextcloud 30.0.1.2 my log was also flooded with the same error message …
After investigating this error I’ve found out that the problem seems to be the network interface (everything after %-sign) of IPv6. The IP-Lib library probably has parsing problems with IPv6 if it contains network interfaces.
As a workaround I’m currently removing the network interface before parsing address string.
In file lib/private/Security/Ip/Address.php replace line 24 containing
$ip = Factory::parseAddressString($ip);
with the following line of code
$ip = Factory::parseAddressString(preg_replace('~%.*$~', '', $ip));
This will remove all network interfaces at the end of string and so IP-Lib is happy …
Hope this helps 
ariaci