Just got some PCBs fabricated which had a failure which turned out to be unconnected ground planes. Why doesn’t KiCad report this in the DRC? Is there a way to make that the case?
Unconnected Items means copper that belongs to a net but isn’t connected to other copper in that net, e.g. missing trace. Your copper island has no net. There’s an option to avoid generating those when creating the fill.
Thanks for the fast response! So, what’s the process for validating this? Do you have to just scrutinise the board and look for air wires? Is this not a common problem or am I doing something wrong?
No, non-zero Unconnected Items means the presence of air wires. You have a different problem. You have generated copper islands.
What I do is not generate islands but look for areas with no ground plane. If the other layer (in my 2 layer board) has ground copper there, I drop a via and then refresh the zone and it will fill. I won’t be able to fill all blank areas but my boards are not that critical. If you need more coverage, then you need a dedicated ground plane layer.
You have a DRC violation, errors and warnings. We don’t know what they are and you can’t expect to get an error free board.
I assume you actually meant to write unconnected ground planes. Is that really so? Is your design sensitive to that? The violation and parity mismatches you didn’t show sound more serious. Parity issue means your layout doesn’t match the schematic so may not work.
I was expecting it to appear as an Unconnected Item in DRC. The other issues are unrelated
(these are complaining about the drill holes I added)
I did mean unconnected, I’ll fix the original post, thanks!
As I said, only copper that belongs to nets are checked for connectivity.
I think you don’t understand the question.
At the picture in first post there is the connection line showing the connection probably from zone to zone. So it is not the problem that checked was not done. The line shows that there is lacking connection but there is nothing listed in Unconnected items. And it is the point of the question.
I have never switched showing errors off so I’m not sure (and can’t check now) but I suppose that if Errors are switched off then Number of Unconnected items is only the number of Warnings about it. As probably no one of unconnected items check is assumed to be the warning (all probably are errors) so you will always get this number equal to 0 when you select to see only warnings.
Are you sure that’s a ratsnest line? Usually ratsnest lines bridge the closest points. Even if it is, it would be from nonet to nonet. But anyway the point is that Unconnected Items doesn’t tell you if there is any unconnected copper. It tells you if all the copper in nets are connected. The question OP is asking is are there any copper islands.
Not 100%, but what another can it be?
If it is about zones I have seen (here at forum) lines connecting surprising points. I have always continuous full layer GND so I have no my own experience what in case of GND islands connection lines are used to show.
10 hours ago (before going to bed) I read your first answer in this thread. I thought that I don’t know where from you know this zones are no net. Is there any guarantee that at such small part of zone you will certainly be shown its net?
No. His question is: I ordered PCB with unconnected islands. Why KiCad didn’t show me that?
So he already knows such islands are there, but don’t know why he see that Unconnected items number is 0.
Because the test doesn’t cover nonet islands. I’m assuming that it’s a nonet island from OP’s description. Otherwise it would be reported as an Unconnected Item, unless there’s a KiCad bug.
But we need clarification from OP: Is it an island and has it not been assigned a net? I usually disable generation of islands. It could be that if one allows island generation, then you get zones with nonet which are not counted as Unconnected Items, and you have to find those some other way.
Which way?
He wrote:
So not no net planes but ground planes.
That’s true, I thought OP showed us all the messages, but OP’s still only showing warnings.
Or he wanted them to be part of the ground plane but didn’t succeed.
As I said we need clarification from the OP, and also the errors, otherwise we’re wasting our time arguing over interpretation of language.
I rather supposed they are gnd. I found that I don’t understand where from you know it is not, but as it was 3 a.m. here I decided to give up and go sleep 
This was the problem! If I tick that I see the errors. Thanks for pointing this out, I am an idiot