simulation with nodes >= 100 doesn't work

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Dear all, I'm simulating a scenario where I have a couple of client-server, and an access point WiFi. In this example, I'm simulating a request-response application, where clients and server send request and response respectively. My problem is that when the nodes' number is greater than or equal to 100 (be careful I'm considering the nodes paired), the communications don't work (i.e. in Wireshark I see just 2 conversations), but when the node numbers is for example 98, it works very well.

Before to post this message, I spent 1 week to read all post in this forum (I also tried to resolve by pre-populating the ARP cache, and read other conversations where is suggested to increase the jitter) without success. Probably could be really a simple thing to resolve but I'm not understanding how. To conclude, I tried an UDP Echo Client-Server application with the same scenario, and I have got the same problem.