What could make a host to be sending arp asking for the mac address of almost al the hosts in the network

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Thanks for your respond.

Is the second part of my question also pointing to the fact that the host is still trying to discover other hosts in the network?

Once a list of valid IP addresses is discovered with arp, each of those hosts is scanned to check for open ports.
Are the SYN packets going to multiple ports on each host?
Is it the same list of ports for each host?

First of all, of all the arp requests sent by the host, only two systems responeded.

to your question, it is different port numbers for each host

Is your wireshark capture on a switch port?
The arp responses are directed so you won't see all the host responses without a span port or network tap.

Yes it is captured on a switch port