As far as I know when you hack a portal there is a certain probability that you get nothing.
As well as there is a probability to get a good loot.
My observations: Hacking enemy portals has a much higher "no item" probability, my estimates would be around 50% Hacking the same portal several times in a row, significantly increases the "no item" probability.
I had an opportunity to hack the same portal 5 times within 30 minutes
(this by the way causes burn out) 2 days in a row, usually at least 2 of later trying (3-5) did not bring me any items except sometimes a portal key.
Portal key has a different "acquire" probability than items I believe if while hacking you jump out of the portal's reach you also get a "no items" message, but I have to test this to confirm
gaming.stackexchange.com/users/11420/BanditoBunny
They are doing this to combat location spoofing.
If your GPS is glitchy or jumps around, this can happen.
If the anti-cheat measures set in you will not be able to do any action (hack, deploy, recharge, link, etc.) for a while.
gaming.stackexchange.com/users/44132/webhax
Speed limit.
I get this message on trains when it reaches a certain speed.
Then I can't hack, attack, deploy, recharge, drop... and so on.
I guess this is to prevent car drivers from playing dangerously.
Once the speed drops under that limit, something Iike 1 minute is required to regain abilities.
gaming.stackexchange.com/users/84447/Vincent
This happens when you're trying to hack above a certain speed.
It is a safety feature to discourage people from trying to focus on hacks while they are speeding down the road.
If you come to a stop, you will be able to hack the portal.
Even if it originally told you the hack acquired no items.
You can immediately hack it again, provided you aren't moving excess of a certain speed.
gaming.stackexchange.com/users/118395/LAvindar
There is 1 portal in my town that always has the no items when quick hacking, at least 9/10 times you go past it.
But if you glyph hack it you get some wonderful stuff.
And this isn't just me it does it to, it seems pretty much everybody who tries it gets the same results
gaming.stackexchange.com/users/128200/joe
As far as I know, this message appears when the game server is overloaded/busy.
What you do is try, and try, and try again, until you get items or until you get the "cooldown active" message.
Because I have received this message over eight times from a portal within a fifteen minute span, I will say that "Hack acquired no items" do not count towards your number of hacks allowed before the portal burns out.
However, I cannot confirm whether "hacking unsuccessful.
cooldown active" does.
gaming.stackexchange.com/users/42471/William C
This just started happening to me.  For a long while I was getting something pretty much every time I hacked a portal.  Tonight I'm frequently getting the message "Hack acquired no items.".  Sometimes it's happened 3 portals in a row.  Is there something that triggers this, or is it just really bad luck tonight?
Why do I keep getting "Hack acquired no items" in Ingress?
gaming.stackexchange.com
<ingress>
gaming.stackexchange.com/questions/95861
gaming.stackexchange.com/users/22491/mmrobins
When you hack a portal you might get nothing. They are doing this to combat spoofing. This happens when you are trying to hack above a certain speed. It is a safety feature. While the most common belief is that you get no items because protections against hacking kicks in, it seems that there might be some other issues regarding that matter.
A user is stating that this is happening because of probability. While the community insists that this happen as a measure to limit speed and hacking. Moreover, there is a user pointing that the servers might be overloaded.