Subnet fully Used, but some of IP addresses not pinging

Subnet fully Used, but some of IP addresses not pinging

Hi team,

Could you please advise on the issue below?
I have some amount of subnets thats show correct results about Used addresses. But one subnet (/23) displayed strange results.
As per OpUtils this subnet fully utilized, all IP addresses in Used state. In fact when I try to ping some addresses from OpUtils it shows that System does not exist. 
As I understood, Used status is IP availability via ICMP. Please correct me if I'm wrong
I tried to do Scan few times, but results still same
So why I can see that my subnet fully utilized if some of IP addresses aren't available via ping?


Best regards

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