The warnings have always existed in /var/log/pihole.log. A change to Pi-hole made them more visible by also printing them into /var/log/pihole-FTL.log and showing them on the dashboard.
The warning you encountered is about a shortcoming of dnsmasq which doesn't fully support alias interface. When you set it to listen on eth0:0 it indeed listens on eth0 instead. This causes the warning you'rev seeing. Your Pi-hole works as you expect it to as it catches the packets on the alias interface because this is still the same physical device.
I prepared a Bugfix for this and gave some more technical details here:
You could try true binding to the alias interface instead, there is a fourth interface listening option for this in the most recent Pi-hole release
Okay got it. Still not sure what to think about those messages put in front so prominent - makes me personally feel a bit uncomfortable tbh. Maybe I just need to get used to this UI change and learn to safely ignore those warnings… which also is not a good behavior I think
No, you can change your configuration to avoid them.
The warning using interface eth0 instead should be resolved in the future when my patch (see PR above) is submitted and accepted in dnsmasq upstream. As said, the warning is just there to notify you that dnsmasq may be behaving differently than you configured it to. If this different behavior is okay for you, that's okay.
The other warning, reducing DNS packet size can be avoided by